IC-NRLF 


ORY 


HERING 


UNIVERSITY  OF  CALIFORNIA 

MEDICAL  CENTER  LIBRARY 

SAN  FRANCISCO 


Ex  Libris 
C.  K.  OGDEN 


MEMORY 

LECTURES  ON  THE  SPECIFIC  ENERGIES 
OF  THE  NERVOUS  SYSTEM 


BY 

PROF.  EWALD.HERING 
I .  -' 

UNIVERSITY  OF  LEIPZIG 


FOURTH  EDITION,  ENLARGED 


1913 

THE  OPEN  COURT  PUBLISHING  COMPANY 
CHICAGO  LONDON 


COPYRIGHT  BY 

THE  OPEN  COURT  PUBLISHING  COMPANY 
1913 


PUBLISHERS'  PREFACE 


DR.  EWALD  HERING,  professor  of  psychology  at  the  Uni- 
versity of  Leipsic,  is  not  a  voluminous  writer,  but  he  has  done 
considerable  work  in  investigating  the  nature  of  specific  color- 
sensations  and  the  processes  of  life.  The  results  of  his 
studies  have  largely  been  accepted  by  his  colleagues  and  his 
little  essay  "On  Memory"  which  contains  a  popular  exposi- 
tion of  this  fundamental  problem  has  become  classical.  Con- 
cerning its  significance  for  physiology,  Prof  Michael  Foster 
of  the  University  of  Cambridge  says  in  the  Encyclopedia 
Britannica,  Vol.  XIX,  page  22: 

"If  the  ingenious  speculations  of  Hering,  that  specific  color- 
sensations  are  due  to  the  relation  of  assimilation  (anabolism) 
to  dissimilation  (katabolism)  of  protoplasmic  visual  sub- 
stances in  the  retina  or  in  the  brain,  should  finally  pass  from 
the  condition  of  speculation  to  that  of  demonstrated  truth, 
we  should  be  brought  face  to  face  with  the  fact  that  the  mere 
act  of  building  up  or  the  mere  act  of  breaking  down  affects 
the  condition  of  protoplasm  in  other  ways  than  the  one  which 
we  have  hitherto  considered,  viz.,  that  the  building  up  pro- 
vides energy  to  be  set  free  and  the  breaking  down  lets  the 
energy  forth.  In  Hering's  conception  the  mere  condition  of 
the  protoplasm,  whether  it  is  largely  built  up  or  largely  broken 
down,  produces  effects  which  result  in  a  particular  state  of 
consciousness.  Now,  whatever  views  we  may  take  of  con- 
sciousness, we  must  suppose  that  an  affection  of  consciousness 
is  dependent  on  a  change  in  some  material.  But  in  the  case 
of  color-sensations  that  material  cannot  be  the  visual  sub- 
stance itself,  but  some  other  substance.  That  is  to  say,  accord- 
ing to  Hering's  views,  the  mere  condition  of  the  visual  sub- 
stance as  distinct  from  a  change  in  that  condition  determines 
the  changes  in  the  other  substance  which  is  the  basis  of  con- 
sciousness. So  that,  if  Hering's  conception  be  a  true  one 


(and  the  arguments  in  favor  of  it,  if  not  wholly  conclusive  are 
at  least  serious),  we  are  led  to  entertain  the  idea  that,  in 
addition  to  the  rough  propagation  of  explosive  decompositions, 
there  are  continually  passing  from  protoplasm  to  protoplasm 
delicate  touches  compared  with  which  the  nervous  impulses 
which  with  such  difficulty  the  galvanometer  makes  known  to 
us  are  gross  and  coarse  shocks.  And  it  is  at  least  possible, 
if  not  probable  (indeed  present  investigations  seem  rapidly 
tending  in  this  direction)  that  an  extension  of  Hering's  view, 
with  such  modifications  as  future  inquiry  may  render  neces- 
sary, to  other  processes  than  visual  sensations,  more  especially 
to  the  inner  working  of  the  central  nervous  system,  may  not 
only  carry  us  a  long  way  on  towards  understanding  inhibition 
and  spontaneous  activity  but  may  lay  the  foundation  of  a 
new  molecular  physiology.  This  however  is  speculative  and 
dangerous  ground,  but  it  seemed  desirable  to  touch  upon 
it  since  it  illustrates  a  possible  or  probable  new  departure. 
What  we  have  said  of  it  and  of  the  more  manageable  mole- 
cular problems  of  physiology  will  perhaps  show  that,  vast  and 
intricate  as  is  the  maze  before  the  physiologist  of  to-day,  he 
has  in  his  hand  a  clue  which  promises,  at  least,  to  lead  him 
far  on  through  it." 

Two  other  popular  expositions  of  highly  important  problems 
in  physiology  have  been  translated  for  the  Open  Court  Pub- 
lishing Company  and  are  included  in  this  edition,  since 
their  extraordinary  significance  renders  it  desirable  that 
they  be  made  accessible  to  the  English  reading  public. 

PAUL  CARUS. 
Chicago,  September,  1913. 


CONTENTS 

LECTURE  I  Page 

MEMORY  AS  A  GENERAL  FUNCTION    -       1 

LECTURE  II 

THE  SPECIFIC  ENERGIES  OF  THE 
NERVOUS    SYSTEM 25 

LECTURE  III 

THE  THEORY  OF  NERVE-ACTIVITY      -     43 

INDEX 71 


MEMORY  AS  A  GENERAL  FUNCTION  OF 
ORGANIZED  MATTER1 


WHEN  a  scientist  leaves  behind  him  his  own  spe- 
cial province  of  inquiry  to  make  an  excursion 
into  the  realm  of  philosophy,  he  may  cherish  the  hope 
of  solving  the  great  problem  which  underlies  the  minor 
questions  to  which  he  has  devoted  his  life,  but  he 
must  be  prepared  for  being  secretly  discredited  with 
those  of  his  colleagues  who  still  remain  quietly  at  work 
with  the  subjects  of  their  specialty,  and  at  the  same 
time  must  expect  the  mistrust  of  the  rightful  represen- 
tatives of  the  empire  of  speculation.  He  runs  the  risk 
of  losing  his  reputation  with  the  former  and  of  gaining 
nothing  with  the  latter. 

The  subject  for  which  I  ask  your  attention  on  this 
occasion  is  a  most  alluring  one;  but  in  accordance 
with  what  I  have  just  said,  it  is  not  my  intention  to 
abandon  the  domain  of  natural  science  to  which  my 
studies  have  been  devoted,  but  only  to  attempt  to  reach 
a  higher  ground  from  which  we  may  enjoy  a  freer  and 
more  general  survey. 

It  will  seem  in  the  course  of  this  paper  as  though 

'An  address  delivered  before  the  Imperial  Academy  of  Sciences,  at 
Vienna,  May  30,  1870. 


2  MEMORY. 

I  am  not  always  faithful  to  this  purpose;  for  I  shall 
often  have  occasion  to  tarry  in  the  province  of  psy- 
chology. Consequently,  for  my  own  justification,  al- 
low me  to  point  out  the  extent  to  which  psychological 
inquiries  form,  not  only  an  allowable,  but  also  an  in- 
dispensable accompaniment  of  physiological  research. 

The  animal  human  organism  with  its  material 
mechanism  is  the  subject  of  physiology.  But  con- 
sciousness is  a  simultaneous  datum.  Besides  the  mov- 
ing of  the  atoms  of  the  brain  according  to  certain  laws, 
the  inner  life  of  our  soul  is  woven  of  sensations  and 
conceptions,  of  feeling  and  will. 

Everyone  experiences  this  in  himself ;  and  it  is  a  fact 
also  which  beams  forth  from  the  faces  of  his  fellow- 
beings.  It  breathes  in  the  life  of  all  higher  organized 
animals,  and  even  the  simplest  creatures  bear  some 
vestiges  of  it.  Who  can  fix  the  limit  of  empsychosis 
in  the  empire  of  organic  nature? 

In  the  face  of  such  a  dual  aspect  of  organic  life 
jvhat  can  physiology  best  do?  Shall  science  be  blind- 
folded on  the  one  side,  in  order  the  better  to  compre- 
hend the  other? 

As  long  as  a  physiologist  is  a  mere  physicist — and 
I  use  the  word  physicist  now  in  its  most  comprehensive 
sense — his  method  of  inquiring  into  organic  nature  is 
altogether  one-sided.  But  it  is  justly  so.  As  a  crystal 
is  to  the  mineralogist,  so  to  the  physiologist  of  this 
class  is  a  man  or  an  animal — a  mere  lump  of  matter. 
An  animal  feels,  of  course,  pleasure  and  pain,  and  with 
the  material  phenomena  of  the  human  body  mental 
emotions  are  connected;  but  that  is  no  reason  why  a 
physicist  should  take  a  different  view  of  the  corporeal 
existence  of  man,  who  to  him  remains  a  compound  of 


MEMORY.  3 

matter  subject  to  the  same  irrefragable  laws  as  stones 
and  plants;  like  a  machine,  his  motions  are  casually 
connected  with  each  other  and  dependent  upon  their 
surroundings. 

Neither  sensation  nor  conception  nor  conscious  will 
can  form  a  link  in  the  chain  of  the  material  processes 
of  which  the  physical  life  of  organisms  consists.  When 
I  answer  a  question,  the  initial  material  process  is  con- 
ducted from  the  organ  of  hearing  by  sensory  nerve- 
fibers  to  the  brain,  and  must  pass  through  it  as  a  ma- 
terial process  in  order  to  reach  the  motor  nerves  of  the 
organ  of  speech.  It  cannot,  after  having  arrived  at  a 
certain  spot  in  the  brain,  enter  into  something  imma- 
terial, in  order  to  be  re-transformed,  in  some  other 
place  of  the  brain,  into  another  material  process.  A 
caravan  in  the  desert  might  just  as  well  enter  the  oasis 
of  a  mirage,  to  return  thence  after  a  refreshing  rest 
into  the  actual  desert. 

Such  is  the  physiologist,  so  far  as  he  is  a  physicist. 
He  stands  behind  the  stage  and  carefully  observes  the 
working  of  the  machinery  and  the  movements  of  the 
actors,  but  he  misses  the  meaning  of  the  action  which 
a  spectator  readily  understands.  Now,  should  a  phys- 
iologist never  be  allowed  to  change  his  point  of  view? 

True,  his  object  is  not  to  understand  a  world  of 
concepts,  but  a  world  of  realities.  Nevertheless,  if 
now  and  then  he  changes  his  point  of  observation  and 
looks  at  things  from  the  other  side,  or  at  least  accepts 
from  trustworthy  observers  the  results  of  their  expe- 
rience, he  will  derive  much  benefit  from  such  an  at- 
titude and  will  better  comprehend  both  the  apparatus 
he  is  studying  and  its  methods  of  working. 

For  this  very   reason  psychology   is   an   indispen- 


4  MEMORY. 

sable  auxiliary  of  physiology.  If  the  latter  science  has 
hitherto  not  made  much  use  of  the  former,  it  has  not 
been  wholly  the  fault  of  physiology.  Psychology  has 
only  lately  worked  her  fields  with  the  plough  of  induc- 
tion, and  it  is  only  in  such  a  soil  that  the  fruits  can  be 
raised  for  which  the  physiologist  has  most  need. 

The  neurologist  is  thus  placed  between  the  phys- 
icist and  the  psychologist.  The  physicist  regards  the 
causal  continuity  of  material  processes  as  the  basis  of 
his  inquiry;  the  thoughtful  psychologist  seeks  for  the 
laws  of  conscious  life,  and  in  so  doing  works  accord- 
ing to  the  rules  of  inductive  methods,  assuming  the  va- 
lidity of  an  inalterable  order.  Now,  if  the  physiologist 
learns  from  simple  self-observation  that  conscious  life 
is  dependent  upon  his  bodily  functions,  and  vice  versa 
that  his  body  to  some  extent  is  subject  to  his  will,  he 
has  only  to  assume  that  this  interdependence  of  mind 
and  body  is  arranged  according  to  certain  laws,  and  the 
link  is  found  which  connects  the  science  of  matter  with 
the  science  of  consciousness. 

Thus  considered,  phenomena  of  consciousness  ap- 
pear to  be  functions  of  material  changes  of  organized 
substance,  and  vice  versa.  As  I  wish  to  avoid  all  mis- 
conceptions, let  me  mention  (although  it  is  included 
in  the  term  function)  that  the  converse  of  this  asser- 
tion means  that  material  processes  of  the  cerebral  sub- 
stance also  appear  to  be  functions  of  the  phenomena 
of  consciousness.  For  if  two  variables  are  dependent 
upon  each  other  according  to  certain  laws,  a  change 
of  the  one  demanding  a  change  of  the  other  and  vice 
versa,  the  one  is  called  a  function  of  the  other. 

This  does  not  mean  that  the  two  variables,  matter 
and  consciousness,  are  connected  with  each  other  as 


MEMORY.  5 

cause  and  effect;  for  we  do  not  know  anything  about 
that.  Materialism  explains  consciousness  as  the  out- 
come of  matter,  idealism  takes  the  opposite  view,  and 
a  third  position  might  postulate  the  identity  of  spirit 
and  matter.  The  physiologist,  as  such,  should  not 
meddle  with  such  questions. 

Aided  by  this  hypothesis  of  a  functional  connec- 
tion between  spiritual  and  material  facts,  modern  phys- 
iology is  enabled  to  bring  the  phenomena  of  conscious- 
ness within  the  domain  of  its  inquiry,  without  leaving 
the  terra  firnia  of  scientific  method.  The  physiolo- 
gist, as  a  physicist,  observes  how  a  beam  of  light,  a 
wave  of  sound,  or  a  vibration  of  heat  affects  the  organs 
of  sensation;  how  they  enter  the  nerves,  are  trans- 
formed into  an  irritation  of  the  nerve-fibers  and  con- 
ducted to  the  brain-cells.  Here  he  loses  all  trace  of 
them.  On  the  other  hand,  he  observes  a  spoken  word 
coming  from  the  mouth  of  a  speaking  person ;  he  sees 
the  person  move  his  limbs,  and  finds  these  movements 
are  caused  by  muscular  contractions  produced  through 
motor  nerves  irritated  by  the  nerve-cells  of  the  central 
organs.  Here  again  he  is  at  his  wit's  end.  The  bridge 
which  should  lead  him  from  the  irritated  sensory  nerve 
to  the  irritated  motor  nerve,  is  indicated  in  the  laby- 
rinthian  connections  of  the  nerve-cells,  but  he  lacks  a 
clue  to  the  infinitely  involved  processes  which  are  in- 
terposed in  this  place. 

It  is  here  the  physiologist  successfully  changes  his 
point  of  view.  Here  matter  no  longer  reveals  the 
secret  to  his  inquiring  glance;  but  he  finds  it  in  the 
mirror  of  consciousness,  not  directly,  but  indirectly  and 
figuratively — yet  in  lawful  connection  with  what  he 
inquires  into.  Here,  in  observing  how  one  idea  re- 


6  MEMORY. 

places  another,  how  conception  rises  from  sensations, 
how  Will  starts  from  conceptions  and  how  emotions 
and  thoughts  interweave,  he  will  suppose  that  there  is 
a  corresponding  series  of  interconnected  material  proc- 
esses accompanying  the  whole  action  of  conscious  life 
according  to  the  law  of  the  functional  interdependence 
of  matter  and  consciousness. 

After  this  introduction  I  may  venture  to  combine 
under  one  point  of  view  a  long  series  of  phenomena 
which  are  apparently  widely  separated  and  belong 
partly  to  the  conscious,  partly  to  the  unconscious  life, 
of  organic  nature.  These  we  shall  consider,  compre- 
hensively, as  the  results  (Aeusserungen)  of  one  and 
the  same  faculty  of  organized  matter,  viz.,  memory,  or 
the  faculty  of  reproduction. 

Memory,  as  generally  understood,  is  merely  the 
faculty  of  voluntarily  reproducing  ideas  or  a  series  of 
ideas.  But  if  faces  and  events  of  past  days  appear, 
uncalled  for,  and  take  possession  of  our  consciousness, 
should  we  not  also  call  this  with  the  same  right,  re- 
membering? We  are  justly  entitled  to  include  in  the 
concept  of  memory  all  involuntary  reproductions  of 
sensations,  conceptions,  emotions,  and  aspirations.  In 
doing  so,  memory  becomes. an  original  faculty,  being 
at  once  the  source  and  unification  of  all  conscious  life. 

It  is  well  known  that  sensuous  perceptions,  if  con- 
stantly repeated  for  a  time,  are  impressed  into  what  we 
call  the  memory  of  the  senses  in  such  a  way  that  often 
after  hours,  and  even  after  we  have  been  busy  with  a 
hundred  other  things,  they  suddenly  return  into  con- 
sciousness in  the  full  sensuous  vivacity  of  their  original 
perception.  We  thus  experience  how  whole  groups 
of  sensations,  properly  regulated  in  their  spatial 


MEMORY.  7 

and  temporal  connections,  are  so  vividly  reproduced  as 
to  be  like  reality  itself.  This  clearly  shows  that  after 
the  extinction  of  conscious  sensations,  some  material 
vestiges  still  remain  in  our  nervous  system,  implying 
a  change  of  its  molecular  and  atomic  structure,  by 
which  the  nervous  substance  is  enabled  to  reproduce 
such  physical  processes  as  are  connected  with  the  corre- 
sponding physical  processes  of  sensations  and  percep- 
tions. 

Every  one  can  observe  in  his  daily  and  hourly  ex- 
perience such  phenomena  of  sense-memory,  although 
in  fainter  forms.  Consciousness  produces  legends  of 
more  or  less  faded  memory-pictures  of  former  sensu- 
ous perceptions.  They  partly  are  called  in  voluntarily, 
and  partly  crowd  in  spontaneously.  Faces  of  absent 
persons  come  and  go  as  pale  and  volatile  shadows,  and 
sounds  of  melodies  which  have  long  died  away  haunt 
us,  if  not  audibly,  yet  perceptibly. 

Of  many  things  and  events,  especially  if  they  have 
been  perceived  only  once  or  very  superficially,  merely 
single,  unusually  striking  qualities  are  reproducible ;  of 
other  things  only  those  qualities  are  reproducible  which 
have  been  remarked  on  former  occasions,  our  brain 
being  in  this  way  prepared  for  their  reception.  Such 
are  responded  to  more  strongly  and  enter  consciousness 
more  easily  and  energetically.  Thus  their  ability  of 
being  reproduced  increases.  In  this  way,  what  is  com- 
mon to  many  things  and  hence  has  been  most  fre- 
quently perceived,  will  by  and  by  be  so  reproducible 
as  to  be  easily  called  forth  by  a  slight  internal  impulse, 
without  any  exterior  and  real  stimulus.  Such  a  sen- 
sation, which  is,  as  it  were,  produced  internally — for 
instance,  the  idea  of  white — is  not  of  the  same  vivacity 


8  MEMORY. 

as  the  sensation  of  white  color  externally  produced  by 
white  light.  But  it  is,  after  all,  essentially  the  same, 
being  a  weak  repetition  of  the  same  material  brain- 
process  and  of  the  same  conscious  sensation.  Thus 
the  idea  of  white  is  an  almost  imperceptibly  weak  per- 
ception. 

In  this  way  the  qualities  which  are  common  to 
many  things  are,  as  it  were,  separated  from  them  in 
entering  our  memory.  They  attain  an  independent  ex- 
istence in  consciousness  as  concepts  or  ideas,  and  the 
whole  rich  world  of  our  concepts  and  ideals  is  con- 
structed of  these  materials  of  memory. 

It  is  easily  seen  that  memory  is  not  so  much  a  fac- 
ulty of  conscious  as  of  unconscious  life.  What  was 
conscious  to  me  yesterday  and  again  becomes  con- 
scious to  me  to-day,  where  has  it  been  in  the  interim? 
It  did  not  exist  as  a  fact  of  consciousness,  and  yet  it 
returned.  Our  concepts  appear  on  the  stage  of  con- 
sciousness only  transiently ;  they  quickly  disappear  be- 
hind the  scenes,  ,to  make  room  for  others.  Only  on 
the  stage  are  they  conceptions,  as  an  actor  is  king  only 
on  the  stage.  As  what  do  they  remain  behind  the 
scenes  ?  For  we  know  that  they  exist  somehow ;  a  cue 
only  is  needed  to  make  them  reappear.  They  do  not 
continue  as  conceptions,  but  as  certain  dispositions  of 
the  nervous  substance  (Stiinmung  der  Nervcnsub- 
stanz)  by  virtue  of  which  the  same  sound  that  was 
produced  yesterday  can  again  be  evoked  to-day. 

Innumerable  reproductions  of  organic  processes  in 
our  cerebral  substance  constantly  combine  with  each 
other,  according  to  certain  laws,  each  in  its  turn  stimu- 
lating another;  but  the  phenomenon  of  consciousness 
is  not  necessarily  joined  with  each  link  of  such  a  series 


MEMORY.  9 

of  processes.  Accordingly,  chains  of  conceptions  some- 
times seem  to  lack  proper  connections  when  conveyed 
to  the  cerebral  substance  through  processes  unaccom- 
pained  by  consciousness.  Therefore,  also,  a  long  se- 
ries of  ideas  may  follow  the  correct  logical  order  and 
have  a  proper  organic  structure,  although  the  differ- 
ent premises  that  are  indispensable  to  such  combina- 
tion do  not  become  conscious  at  all.  Some  ideas 
emerge  from  unconscious  life  into  consciousness,  with- 
out being  connected  with  any  conscious  conception 
whatever;  others  sink  into  unconsciousness  without 
ever  having  been  connected  with  conscious  ideas. 

Between  what  I  am  to-day  and  what  I  was  yester- 
day, a  gap  of  unconsciousness  lies,  the  nocturnal 
sleep ;  and  it  is  only  memory  which  spans  a  bridge  be- 
tween my  to-day  and  my  yesterday.  Who  can  hope  to 
unravel  the  manifold  and  intricately  infertwined  tis- 
sues of  the  inner  life  by  simply  following  the  threads 
of  consciousness  ?  You  may  as  well  gather  your  infor- 
mation about  the  rich  organic  life  of  the  oceanic  world 
from  those  few  forms  which  now  and  then  emerge 
from  the  surface  of  the  sea  merely  to  disappear  again 
into  the  depths  of  the  ocean. 

Thus  the  cause  which  produces  the  unity  of  all 
single  phenomena  of  consciousness  must  be  looked  for 
in  unconscious  life.  As  we  know  nothing  of  this  ex- 
cept wrhat  we  learn  from  our  investigations  of  matter, 
and  since  in  a  purely  empirical  consideration,  matter 
and  the  unconscious  must  be  regarded  as  identical,  the 
physiologist  may  justly  define  memory  in  a  wider 
sense  to  be  a  faculty  of  the  brain,  the  results  of  which 
to  a  great  extent  belong  to  both  consciousness  and  un- 
consciousness. 


10  MEMORY. 

Every  perception  of  an  object  in  space  is  a  highl 
complicated  process.  For  instance,  a  white  ball  sue 
denly  looms  up  before  my  eyes.  It  is  necessary,  IK 
only  to  convey  to  consciousness  the  perception  of  whil 
but  the  circular  periphery  of  the  visible  ball  as  wel 
also  its  globular  form,  as  it  is  recognized  from  the  di: 
tributions  of  light  and  shade;  then  the  exact  distanc 
from  my  eyes  must  be  considered,  and  from  this  \\ 
form  an  estimate  concerning  its  size.  What  an  aj 
paratus  of  sensations,  perceptions,  and  conclusions 
apparently  necessary  for  accomplishing  all  this!  An 
yet  the  actual  perception  of  the  sphere  is  performe 
in  a  few  seconds,  without  my  becoming  conscious  c 
the  single  processes  which  construct  the  whole;  tt 
result  enters  my  consciousness  complete. 

The  nervous  substance  faithfully  preserves  tt 
records  of  processes  often  performed.  All  functior 
necessary  for  correct  perception,  which  at  first  operate 
slowly  and  with  difficulty  with  the  constant  help  of  coi 
sciousness,  are  afterwards  reproduced  summarily  an 
without  an  intensity  sufficient  to  push  each  single  lin 
of  the  chain  beyond  the  threshold  of  consciousnes 
Such  chains  of  unconscious  nerve  processes,  which  ; 
last  end  in  a  link  accompanied  with  consciousnes 
have  been  called  unconscious  chains  of  perceptions,  c 
unconscious  conclusions;  a  name  which  is  justifiafr 
from  the  standpoint  of  psychology.  For  psycholog 
might  frequently  lose  sight  of  the  soul,  if  unconsciot 
states  were  not  taken  into  consideration.  To  a  phy: 
ical  consideration,  however,  unconscious  and  materi; 
mean  the  same,  and  a  physiology  of  the  unconscious 
no  philosophy  of  the  unconscious.2 

2Refers  to  Von  Hartmann's  "Philosophy  of  the  Unconscious." — 7 


MEMORY.  11 

Almost  all  movements  which  man  performs  are  the 
result  of  long  and  difficult  practice.  The  harmonious 
co-operation  of  the  different  muscles,  the  exactly 
gauged  amount  of  work  which  each  one  must  contrib- 
ute to  the  common  labor,  must  be  learned  for  most 
movements  with  great  trouble.  How  slowly  a  begin- 
ner at  the  piano  finds  the  single  notes,  the  eye  direct- 
ing his  fingers  to  the  different  keys,  and  then  how 
marvellous  is  the  play  of  the  virtuoso !  With  the  swift- 
ness of  thought  each  note  finds  an  easy  passage  through 
the  eye  to  the  finger,  to  be  performed  correspondingly. 
One  quick  glance  at  the  music  suffices  to  transform 
into  sound  a  whole  series  of  chords;  and  a  melody 
which  has  been  sufficiently  practised  may  be  played 
while  the  player's  attention  is  directed  to  other  sub- 
jects. 

In  such  a  case  the  will  no  longer  directs  each  sin- 
gle finger  to  produce  the  desired  movements,  and  so 
close  attention  is  not  needed  to  watch  the  whole  execu- 
tion carefully.  The  will  is  only  commander-in-chief. 
The  will  issues  an  order,  and  all  the  muscles  act  ac- 
cordingly. They  continue  to  work  as  long  as  they  move 
in  their  customary  tracks,  till  a  slight  hint  of  the  will 
prescribes  some  other  direction. 

This  would  be  impossible,  if  those  parts  of  the  cen- 
tral nervous  system  which  bring  about  the  movement 
were  not  capable  of  reproducing  entire  series  of  states 
of  irritation.  When  they  have  been  previously  prac- 
tised under  a  constant  accompaniment  of  conscious 
ness,  they  can  be  called  forth,  as  it  were,  independ- 
ently on  the  slightest  impulse  of  consciousness,  being 
executed  more  quickly  and  more  perfectly,  the  oftener 
the  reproductions  have  been  repeated.  All  this  is  pos- 


12  MEMORY. 

sible  only  if  they  remember  what  they  did  before.  Our 
perceptive  faculty  would  forever  remain  in  its  lowest 
stage  if  we  should  consciously  construct  every  single 
perception  from  the  given  single  materials  of  sensa- 
tion. Our  voluntary  motions  would  never  surpass  the 
awkwardness  of  a  child,  if  in  every  case  we  should  re- 
incite  with  conscious  will  the  different  single  impulses 
and  reproduce  over  again  all  our  single  conceptions; 
or,  to  state  it  briefly,  if  the  nervous  motor  system 
were  not  endowed  with  memory,  i.  e.,  an  unconscious 
memory.  What  is  called  "force  of  habit,"  is  the 
strength  of  this  memory. 

It  is  to  memory  that  we  owe  all  we  are  and  have. 
Ideas  and  concepts  are  products  of  it;  each  percep- 
tion, each  thought,  each  motion  is  carried  by  it. 
Memory  unites  all  the  innumerable  single  phenomena 
of  consciousness  into  one  entirety;  and  as  our  body 
would  be  dispersed  into  myriads  of  atoms  if  it  were 
not  held  together  by  the  attraction  of  matter,  so,  but 
for  the  binding  power  of  memory,  consciousness 
would  be  dissolved  into  as  many  fragments  as  there 
are  moments. 

We  have  seen  that  only  a  part  of  the  reproductions 
of  organic  processes,  as  effected  by  the  memory  of 
nervous  substance,  enters  our  consciousness;  no  less 
important  parts  remain  unconscious.  And  the  same 
may  be  proved  by  numerous  facts  relating  to  parts  of 
the  nervous  system  which  are  exclusively  subservient 
to  the  unconscious  processes  of  life.  For  the  memory 
or  reproductive  faculty  of  the  so-called  sympathetic 
nervous  system  is  by  no  means  weaker  than  that 
of  the  brain  and  the  spinal  cord.  Medical  art,  to  a 
great  extent,  makes  good  use  of  this. 


MEMORY.  13 

In  concluding  this  part  of  my  investigation,  let  me 
leave  the  subject  of  nervous  substance  for  a  moment 
in  order  to  take  a  cursory  view  of  other  organic  mat- 
ter, where  we  meet  with  the  same  reproductive  fac- 
ulty, but  in  a  simpler  form. 

Daily  experience  teaches  us  that  muscles  grow 
stronger  the  oftener  they  are  used.  Muscle-fiber,  which 
in  the  beginning  but  feebly  responded  to  the  irritation 
of  a  motor  nerve,  works  with  more  energy  the  oftener 
it  is  irritated,  after  proper  intervals  of  rest.  After  each 
single  action  it  becomes  more  capable  of  action;  it 
grows  fitter  for  the  repetition  of  the  same  work  and 
better  adapted  to  the  reproduction  of  the  same  organic 
process.  Pari  passu,  its  size  increases,  because  it  as- 
similates more  than  in  a  state  of  constant  rest. 

This  is  the  very  same  faculty  of  reproduction  whose 
action  in  nervous  substance  is  so  complicated;  here  it 
is  observable  in  its  simplest  form,  and  easier  under- 
stood as  a  physical  process.  And  what  is  more  accu- 
rately known  of  muscle-substance,  is  more  or  less 
clearly  demonstrable  of  the  substances  of  all  other 
organs.  Everywhere  we  find  an  increased  activity 
with  adequate  pauses  of  rest  accompanied  by  an  in- 
creased strength  of  action ;  and  organs  which  are  used 
oftener  in  the  animal  economy  also  grow  in  size  by 
increased  assimilation.  But  this  increase  of  mass  not 
only  means  an  augmentation  and  growth  of  the  single 
cells  or  fibers  of  which  the  organ  is  composed,  but  also 
an  augmentation  of  their  number.  A  cell  grown  to  a 
certain  size  divides  into  filial  cells,  which  inherit,  in  a 
greater  or  less  degree,  the  qualities  of  the  parental 
cell,  and  accordingly  represents  repetitions  of  it.  This 
growth  and  augmentation  of  cells  is  one  of  the  differ- 


14  MEMORY. 

ent  functions  which  are  characteristic  of  organized 
matter.  These  functions  are  not  only  inferior  phe- 
nomena of  the  cell-substance,  not  only  certain  changes 
or  motions  of  its  molecular  structure,  but  they  also  be- 
come externally  visible  as  a  modification  of  form,  an 
increase  of  size  or  a  division  of  the  cell.  Thus  the 
reproductive  function  of  a  cell  is  manifested  also  as 
a  reproduction  of  the  cell  itself.  This  is  most  obvious 
in  plants ;  the  chief  function  of  their  cells  is  the  work 
of  growth,  while  in  animal  organisms  other  functions 
are  predominant. 

Now,  let  me  finally  consider  the  phenomena  in 
which  the  power  of  memory  in  organized  matter  is  most 
striking. 

On  the  basis  of  numerous  facts,  we  may  justly  as- 
sume that  even  such  qualities  of  an  organism  can  be 
transferred  to  its  posterity  as  have  not  been  inherited 
but  have  been  acquired  under  peculiar  circumstances 
of  life.  Thus,  every  organic  being  endows  its  germs 
with  some  small  inheritance  which  has  been  acquired 
during  the  individual  life  of  the  parental  organism  and 
is  added  to  the  total  legacy  of  the  race. 

Considering  that  properties  are  inherited  which 
have  been  developed  in  different  organs  of  the  paren- 
tal being,  it  has  appeared  highly  enigmatic  to  investi- 
gators how  these  same  organs  could  have  influenced  a 
germ  developed  in  a  distant  place.  So  it  has  happened 
that  as  a  solution  of  this  problem  mystic  views  have 
often  been  propounded. 

The  subject  may  be  best  comprehended  from  a 
physiological  standpoint,  in  this  way. 

The  nervous  system,  in  spite  of  its  being  a  com- 
pound of  many  thousands  of  cells  and  fibers,  never- 


MEMORY.  15 

theless  forms  one  coherent  entirety.  It  is  in  communi- 
cation with  all  organs;  according  to  recent  histolog- 
ical  researches,  it  is  believed  that  it  is  connected  with 
every  cell  of  the  more  important  organs,  either  directly 
or  at  least  indirectly  through  a  living,  irritable,  and 
therefore  conducting  cell-substance.  Through  this 
connection,  all  organs  are  more  or  less  interdependent, 
so  that  the  destinies  of  the  one  are  re-echoed  in  the 
others ;  and  any  irritation  effected  in  any  one,  is  trans- 
fused, be  it  ever  so  feebly,  to  the  remotest  parts  of  the 
body.  In  addition  to  this  delicate  connection  of  all 
parts  of  the  nervous  tissue,  another,  but  slower  and 
more  sluggish,  connection  is  effected  by  means  of  the 
circulating  fluids. 

We  notice  further  that  the  developmental  process 
of  the  germs  destined  to  attain  independent  existence, 
exercises  a  powerful  reaction  on  both  the  conscious 
and  unconscious  life  of  the  whole  organism.  And  this 
is  a  hint  that  the  organ  of  germination  is  in  a  closer 
and  more  momentous  connection  with  the  other  parts, 
especially  with  the  nervous  system,  than  any  other  or- 
gan. Conversely,  the  conscious  and  unconscious  des- 
tinies of  the  whole  organism,  it  is  probable,  find  a 
stronger  echo  in  the  germinal  vessels  than  elsewhere. 

This,  it  must  be  recognized,  is  the  path  on  which 
we  have  to  look  for  the  material  link  between  the  ac- 
quired properties  of  an  organism  and  those  elements 
of  a  germ  that  redevelop  the  parental  qualities. 

You  may  object  that  an  immaterial  something  can- 
not be  determinative  of  the  future  development  of 
germs  so  like  each  other ;  it  must  rather  be  the  peculiar 
character  of  its  material  composition.  But  I  answer: 
The  curves  and  planes  which  a  mathematician  imag- 


16  MEMORY. 

ines,  or  accepts  as  imaginable,  are  more  numerous  and 
manifold  than  the  shapes  of  the  organic  world.  But 
if  we  imagine  infinitely  small  portions  of  all  these  pos- 
sible curves,  they  will  bear  a  closer  resemblance  to 
each  other  than  germs  do.  Nevertheless,  the  whole 
curve  is  latent  in  each  portion  of  it  and  if  a  mathema- 
tician extends  it  in  its  proper  directions,  it  will  grow 
into  the  peculiar  curve  which  was  determined  by  the 
form  of  its  small  fragmentary  part. 

Therefore  it  is  erroneous  to  declare  that  we  cannot 
imagine  such  minute  differences  in  germs  as  must  here 
be  assumed  by  physiology. 

An  infinitely  minute  dislodgment  of  a  point  or  a 
complex  of  points  in  one  part  of  a  curve  will  alter  the 
law  in  its  entire  course.  In  exactly  the  same  way,  an 
evanescent  influence  of  the  parental  organism  upon  the 
molecular  structure  of  its  germ  is  sufficient  to  prede- 
termine its  whole  future  development. 

Accordingly,  the  reappearance  of  properties  of  the 
parental  organism  in  the  full  grown  filial  organism  can 
be  nothing  else  than  the  reproduction  of  such  proc- 
esses of  organized  matter  as  the  germ  when  still  in 
the  germinal  vessels  had  taken  part  in;  the  filial  or- 
ganism remembers,  so  to  .say,  those  processes,  and  as 
soon  as  a  same  or  similar  irritation  is  offered,  a  reac- 
tion takes  place  in  it  just  as  formerly  in  the  parental 
organism,  of  which  it  was  then  a  part,  and  whose  des- 
tinies influenced  it. 

If  in  a  parental  organism  by  long  habit  or  constant 
practice  something  grows  to  be  second  nature,  so  as 
to  permeate,  be  it  ever  so  feebly,  its  germinal  cells, 
and  if  the  germinal  cells  commence  an  independent 
life,  they  increase  and  grow  till  they  form  a  new 


MEMORY.  17 

being,  but  their  single  parts  still  remain  the  substance 
of  the  parental  being,  they  are  bones  of  its  bones,  and 
flesh  of  its  flesh.  If,  then,  the  filial  organisms  repro- 
duce what  they  experienced  as  a  smaller  part  of  a 
greater  whole,  this  fact  is  marvelous  indeed,  but  no 
more  so  than  when  an  old  man  is  surprised  by  remin- 
iscences of  his  earliest  childhood.  Whether  it  still  be 
the  very  same  organized  substance  which  reproduces 
old  experiences,  or  whether  it  be  its  descendant  and 
offspring,  a  part  of  itself,  which  in  the  meantime  ex- 
panded and  grew,  is  a  difference  which,  apparently,  is 
one  of  degree,  not  of  kind.  But  is  it  not  strange  that 
we  are  engaged  in  considering  how  trifling  inheritances 
of  the  parental  organism  can  be  reproduced  in  the 
filial  being,  as  if  we  had  forgotten  that  the  filial  or- 
ganism is  nothing  but  one  great  reproduction  of  par- 
ental organism,  even  in  its  minutest  details?  This  is 
because  we  are  so  accustomed  to  accept  their  similar- 
ity as  granted,  that  we  are  surprised  to  find  a  child 
who  is  in  some  respect  not  quite  like  its  mother,  and 
yet  the  fact  that  it  is  like  its  parent  in  so  many  thou- 
sand ways  is  much  more  wonderful! 

If  the  substance  of  a  germ  is  able  to  reproduce 
what  the  parental  organism  has  acquired  during  its 
individual  life,  how  much  more  will  it  be  able  to  repro- 
duce what  is  innate  in  the  parental  organism  and  has 
been  repeated  through  innumerable  generations  in  the 
same  organized  matter  of  which  the  germ  of  to-day, 
after  all,  is,  and  remains,  but  a  part.  Is  it  then  to  be 
wondered  at,  that  the  things  which  organized  matter 
has  experienced  on  numberless  occasions  are  impressed 
more  strongly  into  the  memory  of  a  germ  than  the  in- 
cidents of  a  single  life?  Every  organic  being  which 


18  MEMORY. 

lives  to-day,  is  the  latest  link  of  an  immeasurable  series 
of  organic  beings,  of  which  one  rose  into  existence 
from  the  other,  and  one  inherited  part  of  the  acquired 
properties  of  the  other.  The  beginnings  of  this  series, 
it  must  be  assumed,  are  organisms  of  extremest  sim- 
plicity, like  those  which  are  known  to  us  as  organic 
germ-cells.  In  consideration  of  this,  the  whole  series 
of  such  beings  appears  as  the  work  of  the  reproductive 
faculty  which  was  inherent  in  the  substance  of  the 
first  organic  form  with  which  the  whole  development 
started.  When  this  first  germ  divided,  it  bequeathed 
to  its  descendants  its  properties;  the  immediate  de- 
scendants added  new  properties  and  every  new  germ 
reproduced  to  a  great  extent  the  modi  operandi  of  its 
ancestors;  part  of  which  grew  feebler,  because  under 
altered  circumstances  their  reproduction  was  no  longer 
elicited. 

Thus  every  organized  being  of  our  present  time  is 
the  product  of  the  unconscious  memory  of  organized 
matter.  Constantly  increasing  and  dividing,  constantly 
assimilating  new  and  excreting  waste  matter,  con- 
stantly recording  new  experiences  in  its  memories, 
to  be  reproduced  again  and  again,  each  has  taken 
richer  and  more  perfect  shape  the  longer  it  has  lived. 

The  whole  history  of  individual  development,  as 
observed  in  higher  organized  animals,  is,  from  this 
point  of  view,  a  continuous  chain  of  reminiscences  of 
the  evolution  of  all  the  beings  which  form  the  ances- 
tral series  of  the  animal.  A  complicated  perception 
takes  place  by  means  of  a  volatile,  and,  as  it  were, 
superficial  reproduction  of  cerebral  processes  which 
have  been  long  and  carefully  practised;  exactly  so  a 
growing  germ  passes  quickly  and  summarily  through 


MEMORY.  19 

a  series  of  phases  which  were  developed  and  fixed, 
step  by  step,  in  the  memory  of  organized  matter  in 
the  series  of  its  ancestral  beings,  during  a  life  of  in- 
calculable duration.  This  view  was  repeatedly  fore- 
shadowed. It  took  shape  in  several  theories;  but  was 
only  rightly  understood  by  a  scientist  of  recent  times. 
For  truth  hides  in  different  shapes  before  the  eyes  of 
its  inquisitors,  until  it  is  revealed  to  the  elect. 

Not  only  is  there  a  reproduction  of  the  outward  and 
inner  conformation  of  body,  organs,  and  cells,  but 
of  its  functions  as  well.  A  chick  emerging  from  its 
shell  at  once  runs  off  as  did  its  mother,  when  she  as  a 
chick  broke  her  shell.  Think  how  extraordinarily 
complicated  are  the  motions  and  sensations  of  such 
acts !  Only  consider  the  difficulty  involved  in  preserv- 
ing equilibrium  in  running,  and  it  will  be  conceded 
that  the  supposition  of  an  innate  reproductive  faculty 
alone  can  serve  as  an  explanation  of  these  intricate 
actions.  The  execution  of  a  motion  that  is  exercised 
during  the  greater  part  of  an  individual  life  becomes 
second  nature,  and  the  actions  of  a  whole  race,  re- 
peated over  and  over  again  by  each  member  of  the 
race,  must  also  become  second  nature. 

The  chick  is  not  only  endowed  with  an  inborn 
dexterity  in  its  motions,  but  possesses  also  a  strongly 
developed  perceptive  faculty.  Without  hesitation  it 
picks  up  the  grains  which  are  thrown  to  it.  This  im- 
plies that  it  sees  them,  and  that  it  correctly  judges 
their  position  and  their  distance;  moreover,  it  has  to 
move  its  head  and  other  limbs  with  great  precision. 
All  these  things  could  not  be  learned  in  the  egg  shell ; 
they  were  learned  from  the  many  thousands  of  beings 
which  lived  before  this  chick,  and  of  which  it  is  the 


20  MEMORY. 

direct  offspring. 

The  memory  of  organized  matter  is  here  most  strik- 
ingly displayed.  The  gentle  stimulus  of  the  rays 
which  proceed  from  a  grain  and  fall  upon  the  retina 
of  the  chicken  gives  occasion  for  the  reproduction  of 
a  complicated  series  of  sensations,  perceptions,  and 
motions,  which  in  this  individual  have  never  as  yet 
been  combined,  and  which,  nevertheless,  were  adjusted 
from  the  beginning  with  accuracy  and  precision,  as  if 
the  animal  itself  had  practised  them  thousands  of 
times.  Such  surprising  performances  of  animals  are 
generally  regarded  as  manifestations  of  instinct;  and 
some  philosophers  have  indulged  in  mystic  explana- 
tions of  instincts.  If  instinct  is  regarded  as  the  result 
of  the  memory  or  reproductive  faculty  of  organized 
matter,  if  we  assume  that  the  race  is  also  endowed 
with  memory,  instinct  is  understood  at  once;  and  the 
physiologist  is  enabled  to  correlate  and  connect  in- 
stinct with  the  great  series  of  facts  we  have  found  to 
be  phenomena  of  the  reproductive  faculty.  In  this 
way  we  have  not  yet  gained,  but  we  have  certainly  ap- 
proached a  physical  explanation  of  the  problem. 

If,  for  instance,  a  caterpillar  changes  into  a  chrys- 
alis, or  a  bird  builds  a  nest,  or  a  bee  constructs  a  cell, 
such  animals,  in  obeying  their  instinct,  act  with  con- 
sciousness, and  are  not  unconscious  machines.  They 
know  to  some  extent  how  to  adapt  their  actions  to 
change  circumstances  and  are  liable  to  err;  they  feel 
pleasure  if  their  work  proceeds,  and  displeasure  if  they 
meet  obstacles.  They  learn  by  working,  it  must  be 
assumed,  and  birds,  no  doubt,  build  their  nests  better 
a  second  time  than  the  first.  But  that  animals  so  easily 
find  the  most  practical  means  of  attaining  their  ends 


MEMORY.  21 

the  very  first  time,  and  that  their  motions  are  so  excel- 
lently and  perfectly  adapted  to  their  purposes,  is  due 
to  the  inherited  disposition  of  the  memory  of  their 
nerve  substance,  which  only  awaits  an  occasion  to 
work  in  full  conformity  with  the  situation,  and  re- 
members just  what  is  necessary  for  that  occasion. 

It  is  striking  how  easily  dexterity  is  acquired,  if  the 
attention  is  sufficiently  confined  to  its  acquisition. 
Specialization  gives  rise  to  proficiency.  He  who  ad- 
mires a  spider  for  spinning  its  web,  should  bear  in 
mind  how  limited  its  other  facilities  are.  Nor  should 
he  forget  that  the  spider  did  not  learn  its  art  by 
itself,  but  this  was  acquired  slowly  by  innumerable 
generations  of  spiders,  and  comprises  almost  all  they 
learned.  Man  took  to  bow  and  arrows  if  his  nets 
failed  to  catch  him  food,  but  the  spider  starved. 

Thus  we  see  the  body  and,  what  is  of  greater  im- 
port, the  whole  nervous  system  of  a  newborn  animal 
is  predetermined  and  predisposed  for  intercourse  with 
the  world  which  it  enters;  it  is  prepared  to  respond 
to  stimuli  and  influences  in  the  same  way  as  this  was 
done  by  its  ancestors. 

We  cannot  expect  that  the  brain  and  nervous  sys- 
tem of  man  should  form  an  exception  to  this  rule. 

True,  man  learns  with  difficulty,  while  the  animal 
from  its  very  birth  is  possessed  of  instinct.  However, 
the  human  brain  at  birth  is  much  farther  from 
its  highest  development  than  the  brain  of  an  animal. 
Its  growth  not  only  takes  a  longer  time,  but  is  much 
more  marked.  The  human  brain,  we  may  say,  is 
much  younger  when  it  enters  the  world  than  the  ani- 
mal brain.  The  animal  is  born  precocious,  and  at  once 
behaves  precociously.  It  is  like  a  phenomenal  child 


22  MEMORY. 

whose  brain  is  overmatured  and,  as  it  were,  too  old, 
so  that  it  is  unable  to  develop  as  luxuriantly  as  an- 
other brain,  which  is  less  finished,  and  inured  to  work, 
but  fresher  and  more  youthful.  The  scope  for  in- 
dividual development  in  the  case  of  the  human  brain, 
and  generally  of  the  human  body,  is  much  larger,  be- 
cause a  relatively  great  part  of  its  development  is 
relegated  to  the  time  subsequent  to  birth.  It  grows 
under  the  influences  of  its  surroundings,  which  affect 
its  senses,  and  acquires  under  such  circumstances,  in 
a  more  individual  way,  what  an  animal  has  received  in 
the  fixed  formation  of  the  race. 

A  far-reaching  memory,  or  reproductive  faculty, 
we  must  assume,  is  to  be  ascribed  to  the  whole  body, 
as  well  as  particularly  to  the  brain  of  a  newborn  man. 
By  the  help  of  this  memory  he  is  able  to  acquire  much 
more  quickly  and  easily  the  attainments  which  were 
developed  in  his  ancestors  thousands  of  times  and  are 
necessary  for  his  life.  What  appears  as  instinct  in 
animals,  in  man  appears,  in  a  freer  form,  as  a  predis- 
position. True,  ideas  are  not  inborn  in  an  infant, 
but  the  ability  of  ready  and  precise  crystalization  of 
ideas  from  a  complex  mixture  of  sensations,  is  due, 
not  to  the  labor  of  the  child,  but  to  the  labor  of  the 
brain-substance  of  innumerable  generations  of  ances- 
tors. 

Theories  of  individual  consciousness,  according  to 
which  it  is  assumed  that  each  human  soul  starts  life 
for  itself  and  commences  a  development  of  its  own,  as 
if  the  thousands  of  generations  before  it  had  not  been 
in  existence,  are  in  striking  disagreement  with  the  facts 
of  daily  experience. 

Those   cerebral   processes   which   elevate   and   dis- 


MEMORY.  23 

tinguish  man,  it  must  be  conceded,  are  not  of  such 
antiquity  as  are  those  connected  with  his  physical 
necessities.  Hunger  and  the  reproductive  instinct 
have  affected  even  the  oldest  and  simplest  forms  of  or- 
ganic beings.  Accordingly,  organic  substance  has  the 
most  powerful  memory  for  these  stimuli,  as  well  as  for 
their  satisfaction.  The  impulses  and  instincts  rising 
from  them  still  exercise  elemental  power  over  the  man 
of  today.  Spiritual  life  grows  slowly,  and  its  most 
beautiful  blossoms  belong  to  the  latest  epochs  of  the 
evolutionary  history  of  organized  matter.  It  is  not 
long  that  the  nervous  system  has  been  crowned  with 
the  glory  of  a  large  and  well-developed  brain. 

Oral  .and  written  traditions  have  been  called  the 
memory  of  mankind,  and  this  conception  is  true.  But 
there  is  another  memory,  which  is  the  reproductive 
faculty  of  the  cerebral  substance.  Without  it,  all 
written  and  oral  language  would  be  empty  and  mean- 
ingless to  later  generations;  for,  if  the  loftiest  ideas 
were  recorded  a  thousand  times  in  writings  or  in  oral 
traditions,  they  would  be  nothing  to  brains  not  predis- 
posed for  them.  They  must  not  only  be  received,  they 
must  be  reproduced.  If  increasing  cerebral  potency 
were  not  inherited  simultaneously  with  the  inward 
and  outward  development  of  the  brain,  with  the  wealth 
of  ideas  which  are  inherited  from  generation  to  gen- 
eration, if  an  increased  faculty  for  the  reproduction 
of  thoughts  did  not  devolve  upon  coming  generations 
simultaneously  with  their  oral  and  written  traditions, 
scripts  and  languages  would  be  useless. 

The  conscious  memory  of  man  comes  to  an  end  with 
his  death;  but  the  unconscious  memory  of  nature  is 
true  and  indestructible.  Whoever  has  succeeded  in  im- 


24  MEMORY. 

pressing  the  vestiges  of  his  work  upon  it,  will  be  re- 
membered forever. 


SPECIFIC  ENERGIES 


THE  SPECIFIC  ENERGIES  OF  THE  NERVOUS 
SYSTEM. 


JOHANNES  MUELLER,  the  greatest  physiologist 
of  our  century,  in  his  essays  on  the  senses,  estab- 
lished a  theory  which  is  well  known  as  "the  theory  of 
the  specific  energies  of  the  sensory  nerves."  I  cannot 
here  recapitulate  his  doctrine  in  his  own  perspicuous 
language,  which  would  be  intelligible  only  to  special- 
ists. But  a  few  sentences  will  suffice  to  explain  the 
quintessence  of  his  theory  to  any  one  whose  occupa- 
tion prevents  him  from  bestowing  more  than  that  kindly 
interest  upon  physiology  which  this  most  fascinating 
science  awakens  in  the  mind  of  every  educated  man. 

From  the  eye  and  from  the  ear,  from  the  mucous 
membranes  of  the  organs  of  taste  and  smell,  and  from 
the  skin  of  the  whole  body,  which  is  the  organ  of  touch 
and  temperature,  proceed  thousands  of  delicate  nerve- 
fibers.  Gradually  uniting,  they  coalesce  into  steadily 
enlarging  bundles,  which  either  lead  directly  to  the 
brain,  or  are  indirectly  connected  with  it  by  the  spinal 
cord.  Through  these  nerve-fibers  the  sensory  organs 
communicate  with  the  brain,  that  most  wonderful  liv- 
ing structure  which  is  both  the  origin  and  the  product 
of  our  consciousness. 

When  a  vibration  of  ether  stimulates  the  nervous 


26  THE   SPECIFIC   ENERGIES. 

membrane  of  our  eye  (the  retina),  a  process  ensues, 
whose  real  nature  we  do  not  yet  understand.  We 
only  know  that  the  stimulation  is  at  once  transmitted 
to  the  fibers  of  the  optic  nerve,  and  in  its  further  prog- 
ress acts  upon  those  cerebral  parts  into  which  the 
optic  nerve  enters.  As  the  life  of  these  brain-struc- 
tures is  in  close  connection  with  our  consciousness,  it 
happens  that  when  a  ray  of  light  enters  the  eye,  it 
causes  an  irritation  of  the  nervous  fibers  and  of  the 
cerebral  cells;  and  thus  we  become  conscious  of  the 
sensations  of  light  and  of  color. 

If  now  these  same  rays,  which  when  entering  the 
eye  produced  the  sensation  of  light,  fall  upon  the  skin 
of  the  hand,  and  there  stimulate  the  delicate  rootlets  of 
the  sensory  nerves,  this  stimulation  is  transmitted 
through  the  nerves  and  the  spinal  cord  to  the  brain,  and 
instead  of  light  we  are  conscious  of  warmth.  How 
is  it  that  the  same  external  agent  in  one  case  produces 
light,  and  in  the  other  warmth  ? 

Moreover,  the  sensation  of  light  can  be  produced 
in  a  perfectly  dark  room  by  stimulating  the  nerves  of 
the  eye  by  an  electric  current ;  and  if  we  pass  the  elec- 
tric current  through  the  auditory  nerve,  we  hear  sounds 
and  noises,  though  the  deepest  silence  surround  us. 
If  we  apply  the  current  to  the  nerves  of  the  skin,  we 
experience  the  sensation  of  heat  or  cold,  although  not 
in  contact  with  any  cold  or  warm  object,  and  if  by 
the  same  current  we  excite  the  nerves  of  the 
tongue,  gustatory  sensations  are  produced.  Accord- 
ingly, the  nervous  apparatus  of  each  sensory  organ  re- 
sponds to  the  same  stimulus  with  different  sensations. 
And  again  we  ask :  How  does  precisely  the  same  cause 
produce  such  a  variety  of  effects? 


THE   SPECIFIC   ENERGIES.  27 

Even  by  the  aid  of  the  microscope  the  anatomist 
has  not  been  able  to  discover  any  essential  difference 
between  the  various  sensory  nerves.  For  instance,  that 
part  of  the  brain  which  produces  the  visual  sensations 
does  not,  in  its  ultimate  structure,  vary  noticeably 
from  those  cerebral  regions  which  produce  sensations 
of  sound  or  temperature.  But  (and  this  is  the  answer 
to  the  problem  in  question)  this  sameness  of  form  is 
not  accompanied  by  a  sameness  of  nature.  The  diverse 
structures  of  the  nervous  system,  the  nerve-cells  and 
the  nerve-fibers,  are  internally  different  in  spite  of  all 
external  similarity,  and  the  diversity  of  the  sensations 
produced  is  a  manifestation  of  such  difference. 

It  is  the  nature  of  the  nerve  substance  in  the  visual 
organ  to  produce  sensations  of  light,  and  only  such. 
It  is  the  bell  which  sounds,  and  not  its  tongue;  and 
similarly  it  is  not  the  vibration  of  ether,  but  the  nerve, 
that  produces  light.  No  matter  whether  it  be  a  ray  of 
light,  whether  it  be  a  pressure  or  a  blow  upon  the  eye, 
an  electric  current,  or  any  stimulus  whatever,  that 
affects  the  nervous  apparatus,  it  invariably  manifests 
itself  as  light  or  color.  In  the  same  way  we  become 
conscious  of  the  stimulations  of  the  auditory  organ 
in  the  form  of  sound  or  noise,  no  matter  what  their 
cause,  which  may  be  aerial  vibrations  or  any  morbid 
irritation  of  the  inner  ear,  or  an  organism  of  the  blood. 

Johannes  Miiller  called  the  inherent  function  of  cer- 
tain nerves  to  communicate  certain  sensations,  not 
otherwise  producible,  to  our  consciousness,  the  "specific 
energy"  of  those  nerves.  More  than  half  a  century 
has  elapsed  since  this  great  physiologist  developed  his 
theory  in  bold  and  magnificent  proportions  thus  form- 
ulating, in  scientific  terms,  an  idea,  the  original  germ  of 


28  THE   SPECIFIC    ENERGIES. 

which  lies  buried  in  the  distant  past,  as  far  back  as 
Aristotle.  Johannes  Miiller's  doctrines  were  re-echoed 
in  innumerable  writings,  but  it  cannot  be  said  that  the 
seed  he  sowed  fell  upon  fertile  soil,  or  that  it  was  de- 
veloped in  any  essential  feature.  A  few  partially  suc- 
cessful attempts  were  made  to  promote  Miiller's  theory 
of  the  sensations  of  color  and  of  sound,  but  aside  from 
that  his  doctrine  bore  little  fruit.  On  the  contrary  it 
was  suppressed  even  by  Johannes  Miiller's  own  dis- 
ciples. It  again  became  customary  to  regard  all  nerve- 
fibers  as  having  essentially  the  same  nature,  and  to 
suppose  that  the  same  kind  of  stimulation  is  transmit- 
ted in  all  fibers  of  the  various  nerves.  The  question 
why  the  nerves  of  the  various  sensory  organs  produce 
such  different  sensations  was  either  entirely  abandoned, 
or  it  was  deemed  sufficient  to  say  that  the  cause  should 
be  sought  in  the  brain,  although  the  same  reasons  which 
were  thought  to  prove  that  all  nerve-fibers  are  of  the 
same  nature,  would  hold  good  also  in  the  case  of  the 
brain  cells  and  fibers.  Even  in  some  writings  of  the 
present  day  we  meet  with  authors  who,  confounding 
philosophy  and  physiology,  declare  that  the  theory  of 
specific  energies  is  one  of  the  great  aberrations  of 
physiology. 

In  consideration  of  this  fact,  permit  me,  as  an  en- 
thusiastic follower  although  not  a  personal  disciple  of 
the  great  scientist,  to  disclose  and  reveal  the  deep 
significance  of  the  master's  doctrine,  and  to  show 
that  it  is  the  application  of  a  principle  which  has  been, 
or  surely  will  be,  accepted  in  other  provinces  of  bi- 
ology. 

The  animal  kingdom  exhibits  an  inexhaustible  mul- 
tiplicity of  form,  and  to  a  layman  who  is  not  initiated 


THE   SPECIFIC   ENERGIES.  29 

into  the  science  of  biology  it  seems  almost  incredible 
that  living  creatures  so  variously  different  in  their 
forms  and  habits,  should  be  so  identical  in  form  as 
germs  in  the  first  stage  of  their  development!  As  a 
rule,  even  the  most  experienced  eye,  with  the  assist- 
ance of  every  means  of  scientific  analysis,  would  not 
be  able  to  recognize  in  a  germ  the  animal  into  which 
it  is  going  to  develop.  The  fish  as  well  as  the  bird, 
and  the  insect  as  well  as  man,  so  far  as  we  can  judge 
from  external  appearances,  all  begin  their  lives  as  very 
simple  and  microscopically  small,  spheroidal  struc- 
tures. Nor  does  this  uniformity  exist  only  for  the  eye ; 
for  chemical  analysis  resolves  them  all  into  the  same 
ultimate  elements. 

We  ask,  how  is  it  possible  that  totally  different 
forms  can  develop  from  apparently  similar  germs ;  and 
the  answer  is,  that  this  resemblance  of  the  germs  is 
merely  external.  By  the  aid  of  the  most  powerful 
microscopes  we  can  barely  discern  the  roughest  out- 
lines of  their  structures. 

In  the  heavens  whole  systems  of  suns  appear  only 
as  nebulas,  which  even  the  most  powerful  telescopes 
cannot  resolve  into  single  stars.  As  observation  is 
impossible,  we  can  only  surmise  their  structure.  Simi- 
larly the  ultimate  and  exquisitely  delicate  framework 
in  the  achitecture  of  the  living  substance  of  germs  is 
withdrawn  from  the  observation  of  even  the  minutest 
research.  Could  we  approach  nearer  and  nearer  to 
one  of  these  nebulas,  one  star  after  the  other  would 
emerge  from  the  apparently  homogeneous  mass;  we 
should  see  planets  revolving  around  their  suns,  and 
satellites  about  the  planets.  Thus,  if  with  our  corporeal 
or  intellectual  eye  we  could  penetrate  the  minutest  in- 


30  THE    SPECIFIC    ENERGIES. 

ternal  structure  of  the  substance  of  germs — if  we  could 
comprehend  the  arrangement  and  motion  of  the  mole- 
cule and  atoms — we  should  discover  that  the  living 
germ-substance  of  each  animal  species  has  its  specific 
properties,  and  the  substance  of  each  single  germ  has 
its  individual  properties  by  virtue  of  which,  in  a  fur- 
ther evolution,  a  special  and  peculiar  type  must  me« 
chanically  develop. 

Whether  these  internal  variations  of  the  germs  are 
chemical  or  physical  is  at  present  immaterial;  for 
the  physical  properties  of  a  substance  are  conditioned 
by  their  chemical  qualities,  and  when  we  inquire  into 
the  molecular  and  atomic  structure  of  a  substance  the 
dividing  line  between  the  domains  of  chemistry  and 
physics  entirely  disappears.  We  cannot  in  the  im- 
mediate future,  however,  hope  to  find  a  chemical  for- 
mula for  the  individual  germ  substances.  To  reveal 
the  delicate  secret  of  living  matter  by  the  compara- 
tively crude  methods  of  chemistry  would  be  like  try- 
ing to  explain  the  mechanism  of  a  watch  by  melting  it 
in  a  crucible  and  examining  the  molten  mass  with  re- 
spect to  its  ingredients. 

As  we  cannot  at  present  solve  the  problem  of  the 
internal  variation  of  the  externally  similar  germ-sub- 
stances, we  must  be  satisfied  with  the  statement  that 
the  germs  of  each  animal  species  possess  an  inherent 
and  innate  faculty — i.  e.,  a  specific  energy,  which  di- 
rects its  developments  in  a  manner  characteristic  of 
this  animal  and  of  no  other.  Again,  each  single  germ 
possesses  an  individual  energy  which  in  addition  to 
the  normal  features  of  its  species  secures  an  individual 
character  to  its  future  development. 

Let  us  now  approach  our  problem   from  another 


THE   SPECIFIC  ENERGIES.  31 

side.  When  the  naked  eye  is  not  able  to  discern  the 
more  minute  organization  and  delicate  structure  of  an 
organism,  the  anatomist  employs  the  microscope,  and 
a  new  world  of  discernible  facts  is  revealed  to  him. 
The  apparently  homogeneous  form  dissolves  into  in- 
numerable distinct  structures ;  millions  of  the  minutest 
separately-existing  beings,  different  in  shape  and  in- 
ternal structure,  compose  a  systematically  arranged 
aggregate,  thus  forming  the  diverse  organs ;  and  these 
beings,  in  spite  of  the  complicated  interdependence, 
lead  quite  separate  lives,  for  each  single  being  is  an 
animated  center  of  activity.  The  human  body  does 
not  receive  the  impulse  of  life  like  a  machine  from  one 
point,  but  each  single  atom  of  the  different  organs 
bears  its  vitalizing  power  in  itself.  The  current  of 
life  does  not  emanate  from  one  special  part  of  the 
body,  but  all  its  minutest  parts  are  themselves  sources 
of  life.  The  architecture  of  the  human  body,  which 
consists  of  these  elementary  organisms,  or  cells  as 
they  are  called,  has  often  been  explained.  The  har- 
monious interaction  and  the  division  of  labor  among 
these  innumerable  particles  has  been  compared  to  the 
judiciously  adapted  co-operation  of  the  individual 
members  of  a  well-regulated  community.  As  in  such  a 
community,  so  also  in  the  human  organism,  a  special 
kind  of  work  is  assigned  to  each  group  of  individuals, 
and  according  to  the  various  functions  the  elemen- 
tary organisms  are  differently  formed;  but  those  ele- 
ments which  possess  the  properly  so-called  vital  power, 
in  every  respect  exhibit  the  most  striking  resemblance, 
although  it  may  be  hidden  by  and  interwoven  with 
various  less  important  solid  or  fluid  ingredients. 

In  all  living  cells  and  fibers  of  the  different  organs 


32  THE   SPECIFIC   ENERGIES. 

we  encounter  the  same  colorless  viscous,  almost  fluid, 
soft  unstable  substance,  in  the  shape  of  highly  delicate 
threads,  nets,  or  drops.  It  is  the  vital  elements  of  the 
cell.  There  the  enigma  of  life  lies  hidden,  for  this 
viscous  substance  is  the  moving  and  creating  power  in 
the  elementary  organism.  It  produces  the  contrac- 
tion of  muscular  fibers  and  transmits  the  irritation  in 
the  nerve-fibre ;  it  builds  up  the  solid  and  strong  mass 
of  the  supporting  bone  and  the  tough  fibre  of  the  ten- 
don it  shapes  the  feathers  of  the  bird,  the  scales  of  the 
fish,  and  the  horns  of  the  stag. 

Yet  it  is  everywhere  apparently  the  same,  and  if 
it  is  isolated  from  its  proper  sphere  and  surroundings, 
and  considered  by  itself,  the  most  experienced  eye  can- 
not tell  which  of  the  different  functions  was  performed 
by  it. 

Again  we  ask,  how  is  it  possible  that  apparently 
equal  causes  produce  such  different  effects.  Here  no 
one  will  doubt  that  in  spite  of  external  similarity  the 
living  substance  in  the  cells  of  the  individual  or- 
gans is  internally  different,  and  a  difference  of  func- 
tion necessarily  results  from  this  difference  of  internal 
structure.  It  is  an  innate  function.  The  specific 
energy  of  the  living  substance  in  the  liver  produces 
bile,  as  the  specific  energy  of  the  root  of  a  hair  builds 
up  the  horny  mass  of  hair. 

All  the  innumerable  elementary  beings  or  cells  of 
an  organism  are  the  offspring  of  one  single  germ-cell 
in  which  the  development  commenced.  By  division, 
the  first  cell  was  split  in  two.  Although  both  were 
intimately  connected  with  each  other,  they  were  never- 
theless, to  a  certain  extent,  independent  cells.  These 
two  cells  divided  again  and  formed  other  cells,  and  so 


THE   SPECIFIC   ENERGIES.  33 

on.  Thus,  by  a  constantly  renewed  formation  of  more 
living  substance  the  number  of  the  elementary  struc- 
tures increases  in  almost  inexhaustible  multiplicity. 
But  in  the  progress  of  multiplication  the  form  and 
arrangement  of  the  cells  are  also  changed.  They 
separate  into  various  homogeneous  groups,  each  of 
which  differs  from  the  others  in  character  in  so  far 
as  it  performs  a  special  function.  The  living  substance 
is  specialized  in  the  process  of  development  according 
to  its  function  and  destination.  All  the  united  differ- 
ent specific  energies  which  later  on  will  separately  de- 
velop to  full  life  in  its  descendants,  lie  concealed,  al- 
though only  potentially,  in  the  substance  of  the  germ. 

In  the  light  of  these  considerations  the  diversity  of 
function  in  the  nervous  substance  can  no  longer  sur- 
prise us.  Its  external  similarity  prevents  us  from 
considering  it  as  internally  different  and  from  claim- 
ing for  it  specific  energies  according  to  the  doctrine 
of  Johannes  Miiller. 

The  specific  energies  of  the  living  substance  in  the 
different  organs  are  characterized  by  their  chemical  or 
physical  functions ;  while  in  the  present  state  of  science 
the  energies  of  the  nervous  substance  can  be  recog- 
nized only  by  the  different  sensations  which  they  pro- 
duce in  our  consciousness.  Our  sensations  and  all  the 
phenomena  of  consciousness  are  the  psychological  ex- 
pressions of  physiological  processes  or  the  stimulations 
of  our  nerves, — especially  of  our  brain.  Vice  versa, 
these  stimulations  are  the  material  expression  of  the 
processes  in  our  soul. 

The  soul  does  not  act  unless  the  brain  is  in  action 
at  the  same  time.  Whenever  the  same  sensation  or  the 
same  thought  recurs,  a  certain  physical  process  which 


34  THE   SPECIFIC  ENERGIES. 

belongs  to  this  special  sensation  or  thought  is  re- 
peated ;  for  both  are  inseparably  connected.  They  are 
conditioned  by  and  productive  of  each  other.  Accord- 
ingly, from  the  course  of  our  sensations  we  can  draw 
inferences  concerning  the  simultaneous  and  corre- 
sponding course  of  processes  in  the  brain.  The  reso- 
lution of  our  sensations  into  their  various  elements  is 
at  the  same  time  an  analysis  of  the  involved  interac- 
tions of  the  various  elementary  cerebral  functions  or 
stimulations. 

For  instance,  let  us  suppose  that  the  great  variety 
of  the  sensations  of  light  and  color  can  be  reduced  to 
a  few  simple  or  elementary  sensations,  to  those  of  the 
principal  colors,  which  by  combining  in  different  pro- 
portions can  produce  innumerable  different  sensations. 
This  fact,  if  proved,  would  justify  the  conclusion  that 
different  kinds  of  elementary  stimulations  can  take 
place  also  in  the  nerve  substance  of  the  visual  organ. 
Each  of  them  corresponds  to  one  of  the  elementary 
sensations,  and  the  elementary  stimulations  can  be  ar- 
ranged in  a  manner  analogous  to  that  of  the  elemen- 
tary sensations.  Or  similarly,  if  we  succeed  in  reduc- 
ing all  the  many  and  various  gustatory  sensations  to  a 
few  simple  sensations,  we  may  again  justly  infer  that 
a  corresponding  number  of  elementary  irritations  can 
be  produced  in  the  nerve-substance  of  the  tongue. 

Consequently  the  analysis  of  our  sensations  leads 
us  to  recognize  the  fact  that  what  Johannes  Miiller 
summarily  called  the  specific  energy  of  a  sensory  nerve 
may  be  resolved  into  a  certain  number  of  elementary 
irritations.  But  we  need  not  assume  that  a  distinct 
nerve-element  is  a  medium  for  each  simple  irritation. 
The  same  nerve-cell  can  produce  the  sensation  of  heat 


THE   SPECIFIC  ENERGIES.  35 

or  of  cold  according  to  the  direction  in  which  its  spe- 
cific energy  is  stimulated.  The  same  fiber  of  the  visual 
organ  can  be  stimulated  in  different  ways  and  thus  con- 
vey correspondingly  different  sensations  of  color. 

Each  single  kind  of  stimulus,  therefore,  does  not 
necessarily  correspond  to  one  and  the  same  nerve 
substance.  The  specific  energy  of  a  certain  nerve- 
element  is  not  merely  a  simple  property,  it  is  not  a 
faculty  which  causes  only  one  kind  of  function,  it  is  a 
multiform  potency. 

The  power  of  specializing  and  individualizing  its 
functions  is  an  inborn  quality  of  living  substance,  and 
bears  its  richest  and  most  wonderful  fruit  in  the  ner- 
vous system.  In  this  respect  the  nervous  system  far 
surpasses  all  other  organs. 

One  fiber  of  a  muscle  performs  the  same  function 
as  all  its  other  fibers,  and  even  the  fibers  of  different 
muscles  possess  essentially  the  very  same  energy.  One 
liver-cell  works  as  all  the  other  liver-cells  do,  and  it 
cannot  work  otherwise.  The  intensity  of  a  function 
may  be  different  in  the  different  fibers  or  cells  of  such 
an  organ,  but  the  kind  of  function  is  common  to  all. 

Not  so  in  the  nervous  system.  The  various  ener- 
gies in  the  various  groups  of  the  nervous  elements  are 
innate.  By  an  innate  faculty  the  optic  nerve  of  the 
new-born  babe  responds  to  the  ray  of  light  which  en- 
ters the  eye  with  a  sensation  of  light,  and  the  nerve  of 
the  skin  responds  to  an  increase  of  temperature  with 
a  sensation  of  warmth. 

The  specific  energy  of  almost  all  other  organs  is 
definitely  fixed  at  the  time  of  birth  and  will  change  in 
the  further  development  of  life  in  degree  only — but 
never  in  character. 


36  THE    SPECIFIC   ENERGIES. 

The  muscle-fiber  of  a  babe  contracts  in  the  same 
way,  and  thus  exhibits  the  same  energy,  as  does  the 
muscle-fiber  of  an  adult  person.  The  liver-cell  of  an 
old  man  produces  bile  just  as  does  the  liver-cell  of  a 
child.  The  muscle  and  the  liver  grow  with  the  entire 
man,  but  the  fibers  and  cells  added  can  always  per- 
form only  one  and  the  same  function.  Some  fibers 
and  cells  perish  in  the  course  of  life,  but  those  which 
take  their  place  merely  perform  the  functions  of  the 
replaced  fibers  and  cells. 

Thus  the  innate  energy  of  almost  all  organs  re- 
mains unchanged  throughout  life.  The  small  individu- 
al cell-organisms  of  which  the  organs  consist,  come 
and  go,  one  generation  follows  another,  in  some  organs 
more  rapidly  and  in  others  more  slowly.  The  living 
substance  of  each  single  element  is  consumed  and  then 
replaced  by  nutrition,  but  their  character  and  activity 
always  remain  the  same.  In  the  nervous  system  all 
this  is  very  different.  Although,  as  a  rule,  the  innate 
energies  of  many  regions,  especially  in  the  peripheral 
nervous  system,  remain  unchanged  throughout  life, 
there  is  in  the  nervous  system  of  a  new-born  babe 
some  living  substance  which  is  ready  to  be  moulded 
for  the  performance  of  this  or  that  function  and  for  the 
development  of  this  or  that  individual  energy. 

Above  all,  the  brain  of  a  new-born  babe  is  not  a 
completed  structure.  It  grows  and  develops ;  and  when 
the  externally  visible  growth  has  reached  its  limits,  the 
internal  process  of  formation  continues.  Up  to  the 
moment  of  birth  the  nervous  system  with  the  brain  is 
developed  according  to  its  own  inner  law.  Until  then, 
neither  light  nor  sound  nor  any  other  sensory  stimulus 
has  affected  the  nerves,  and  the  brain  has  been  asleep. 


THE   SPECIFIC   ENERGIES.  37 

After  birth  thousands  of  new  stimuli  at  once  intrude 
from  the  external  world  upon  the  nervous  system.  The 
eye  is  opened  to  the  vibrations  of  ether  and  sound- 
waves obtrude  upon  the  ear ;  pressure  and  impact,  cold 
and  warmth  affect  the  skin — thus  placing  the  brain 
which  heretofore  was  left  to  itself,  under  the  influence 
and  discipline  of  the  external  world. 

Before  birth  the  chemical  processes  of  the  nervous 
system,  its  change  of  matter  and  its  growth,  depended 
upon  internal  conditions  of  life.  After  birth  the  stimuli 
of  the  external  world  excite  the  brain  and  produce 
a  more  vigorous  exchange  of  matter  for  further  de- 
velopment an'd  increase  of  the  living  substance.  The 
further  development,  the  inner  formation  and  cultiva- 
tion henceforth  depend  upon  occurrences  in  the  ex- 
ternal world  which  the  brain  experiences. 

All  living  substance,  especially  nerve-matter,  has 
the  peculiarity  that  every  stimulation  produced  in  a 
limited  region  at  once  spreads  to  the  adjoining  parts. 
It  continues  spreading  as  long  as  it  meets  with  any  sub- 
stance which  is  capable  of  being  similarly  stimulated 
and  which,  so  to  speak,  responds  to  such  stimulation. 

The  specific  stimulation  awakened  in  the  sensory 
nerves  by  external  causes, -is  thus  transmitted  to  the 
virgin  parts  of  the  brain.  Here  the  stimulation  ter- 
minates in  the  most  youthful  and  most  docile  living 
substance,  and  here  every  kind  of  stimulation  finds 
its  echo.  For  this  substance  which  possesses  no  innate 
and  definitely  specialized  energy,  has  not  yet  lost  its 
susceptibility  for  all  other  stimulations  through  the 
frequent  repetition  of  a  certain  kind  of  stimulation. 

If  the  virgin  substance  of  the  brain  is  excited  and 
internally  agitated  by  a  stimulation  which  has  been 


38  THE    SPECIFIC   ENERGIES 

transmitted  through  the  nerve-fibres  of  the  sensory 
organs,  an  increased  ability  to  reproduce  the  same  kind 
of  stimulation  is  acquired  by  a  permanent  change  of  its 
internal  structure.  If  the  sensory  nerve  again  trans- 
mits the  same  stimulation,  the  cerebral  substance  re- 
sponds to  it  more  easily.  The  oftener  it  is  repeated, 
the  stronger  will  grow  the  inclination  to  reproduce  just 
this  kind  of  stimulation.  Through  frequent  repetition, 
one  particular  kind  of  function  becomes,  as  it  were, 
the  second  nature  of  a  single  cerebral  cell,  i.  e.,  the 
cell  acquires  this  special  ability  or  energy.  In  this  way 
the  individual  energies  of  the  cerebral  cells  and  fibers 
are  developed  by  education  on  the  basis  of  the  inher- 
ited dispositions.  Also  the  additional  energy  which 
the  cells  acquire  during  life  is  transmitted  by  inheri- 
tance to  the  new-formed  cells  generated  by  partition. 
These  new  cells  can  in  their  turn  develop,  evolve,  or 
modify  the  inherited  energy. 

The  anatomical  arrangement  of  the  brain  is  such 
as  to  place  (single)  parts  of  the  so-called  gray  sub- 
stance into  a  particularly  intimate  relation  with  special 
sensory  nerves.  The  stimulation  of  a  sensory  nerve- 
fiber  will  necessarily  seize  upon  and  affect  those  cere- 
bral cells  first  which  are  in  closest  connection  with  it. 
But  each  cerebral  cell  is  connected  with  other  cerebral 
cells  by  a  net-work  of  most  delicate  nerve-fibers. 

The  stimulation  which  enters  from  the  sensory  nerve- 
fibers  into  the  gray  substance  can  advance  (through 
those  cerebral  elements  which  are  excited  first)  in  all 
directions  farther  and  farther  into  the  labyrinth  of  the 
cerebral  cells  and  fibers,  until  at  last  it  dies  out  and 
ceases  sooner  or  later,  or  calls  forth  new  stimulations 
in  exchange,  which  start  from  the  brain  and  return  to 


THE   SPECIFIC  ENERGIES.  39 

the  peripheral  nervous  system. 

Every  cerebral  element  is  subject  to  the  educating 
influence  of  those  sensory  nerve-fibers  with  which  it  is 
anatomically  connected  and  whose  energies  are  most 
closely  related  to  it.  But  these  single  cerebral  ele- 
ments can  also  receive  stimulations,  although  in  a 
weaker  degree,  from  the  adjoining  fibers  of  the  same 
sensory  nerve  and  even  from  those  nerve-fibers  which 
enter  the  gray  substance  in  more  remote  parts  and 
originate  in  other  sensory  organs. 

In  this  way  the  cerebral  substance  is  constantly 
permeated  with  many  diverse  stimulations  crowding 
upon  it  from  all  the  sensory  regions.  The  cerebral  cell 
will  be  particularly  educated  for  the  qualities  of  these 
stimulations  according  to  its  opportunity  of  easily  and 
repeatedly  receiving  stimulation  from  this  or  that  sen- 
sory organ  and  from  such  or  such  a  sensory  nerve- 
fiber.  It  will  acquire  the  faculty  of  reproducing  them 
vigorously,  as  often  as  any  stimulus  is  offered,  no  mat- 
ter how  weak  it  may  be. 

Consequently,  every  single  cerebral  element  attains 
an  individual  character  in  the  course  of  its  develop- 
ment and  under  the  influence  of  sensory  experience. 
And  it  may  be  asserted  that  not  even  two  of  the  nu- 
merous cerebral  cells  are  alike  in  kind  and  degree 
of  individual  energy.  If  one  cerebral  cell  is  destroyed, 
there  would  of  course  be  many  others  which  possess 
in  all  essential  points  the  same  energy,  and  can  by 
their  functions  compensate  its  loss,  but  no  other  cere- 
bral element  could  do  exactly  the  same  work  with  ex- 
actly the  same  individual  ability,  with  the  same  ease 
and  exactness;  just  as  no  man  can  in  all  respects  en- 
tirely replace  another  man. 


40  THE    SPECIFIC    ENERGIES. 

Experience  and  practice  rest  upon  this  specializa- 
tion and  individualization  of  the  functions  in  the  differ- 
ent cerebral  elements,  and  the  energies  of  the  nerve 
substance  which  are  developed  in  the  course  of  our 
life  are  the  organic  expression  of  individual  memory. 

The  nervous  system,  and  above  all  the  brain,  is  the 
great  tool-house  of  consciousness.  Each  one  of  the 
cerebral  elements  is  a  particular  tool.  Consciousness 
may  be  likened  to  a  workman  whose  tools  gradually 
become  so  numerous,  so  various,  and  so  specialized 
that  for  every  detail  of  his  work  he  has  a  tool  specially 
adapted  to  perform  just  this  kind  of  work  most  easily 
and  accurately.  If  he  loses  one  of  his  tools,  he  still 
possesses  a  thousand  other  tools  to  do  the  same  work 
although  with  more  difficulty  and  loss  of  time.  Should 
he  lose  these  thousands  also,  he  might  retain  hundreds, 
with  which  he  can  possibly  do  his  work  still,  but  the 
difficulty  increases.  He  must  have  lost  a  very  large 
number  of  his  tools,  if  certain  actions  became  abso- 
lutely impossible. 

The  knowledge  of  the  tools  alone  does  not  suffice 
to  ascertain  what  work  is  performed  by  the  tools.  The 
anatomist,  therefore,  will  never  understand  the  laby- 
rinth of  cerebral  cells  and  fibers,  and  the  physiologist 
will  never  comprehend  the  thousand-fold  intertwined 
actions  of  its  stimulations,  unless  they  succeed  in  re- 
solving the  phenomena  of  consciousness  into  their  ele- 
ments in  order  to  obtain  from  the  kind  and  strength, 
from  the  progression  and  connection  of  our  percep- 
tions, sensations,  and  conceptions,  a  clear  idea  about 
the  kind  and  progression  of  the  material  processes  in 
the  brain.  Without  this  clue  the  brain  will  always  be 
a  closed  book  to  us. 


THEORY    OF   NERVE   ACTIVITY.  41 

We  can  indeed  compare  the  brain  to  a  book.  A 
book  is  anatomically  a  number  of  rectangular  white 
leaves,  bound  on  one  side,  and  marked  on  their  pages 
with  numerous  black  spots  of  different  form  and  size. 
Under  a  microscope,  the  leaves  will  be  seen  to  consist 
of  delicate  fibers,  and  the  black  spots  of  minute  black 
granules.  A  chemical  analysis  will  show  that  the 
leaves  are  cellulose,  the  spots  carbon  and  resinous  oil. 
If  all  this  has  been  investigated  and  ascertained  with 
the  utmost  accuracy,  we  do  not  know  in  the  least 
why  the  black  spots  are  arranged  just  in  this  and  in 
no  other  way,  why  some  spots  are  large  and  others 
small,  why  some  occur  frequently,  others  rarely,  why 
the  single  leaves  follow  one  another  in  this  and  in  no 
other  order,  and  altogether  what  the  whole  book  really 
means. 

Whoever  wishes  to  know  what  the  book  signifies, 
must  know  the  function  of  the  specific  energy  of  each 
single  letter  and  of  the  individual  energy  of  each 
single  word — in  short,  he  must  know  how  to  read. 

Nothing  can  be  fully  explained  by  analogy,  and  it 
is  perhaps  dangerous  to  attempt  to  adorn  the  dry  lan- 
guage of  science  with  allegories. 

But  let  the  scientist  wear  his  working  apparel  while 
ploughing  the  field  of  his  science;  and  when,  on  a 
festive  occasion  he  offers  the  fruits  of  his  labor  to 
others,  he  should  be  welcome  in  holiday  attire. 


NERVE  ACTIVITY 


ON  THE  THEORY  OF  NERVE-ACTIVITY1 


44  A  THEORY  of  nerve-energy  would  have  to 
JLJL  show  how  precisely  those  properties  which 
are  characteristic  of  the  activity  of  the  nerves  result 
with  necessity  from  the  multifarious  aggregate  of  the 
conditions  constituting  them." 

I  have  taken  these  words  from  the  Manual  of  Physi- 
ology of  Carl  Ludwig,2  that  memorable  man  who 
achieved  so  much  for  physiology  during  his  long  con- 
nection with  the  university  of  Leipsic.  And  now  that 
I  am  about  to  develop  a  special  view  of  my  own  relating 
to  nerve-activity,  it  is  both  appropriate  and  requisite 
that  I  should  apply  the  criterion  involved  in  Carl  Lud- 
wig's  words  to  the  theory  which  I  am  to  advance. 

If  I  were  asked  whether  this  view  could  be  consid- 
ered as  a  contribution  to  the  theory  of  nerve-activity  in 
the  sense  indicated  by  that  great  master  of  experimental 
physiology,  I  should  have  to  confess  that  such  is  not 
the  case ;  for  neither  from  their  constitution  nor  from 
their  form  am  I  compelled  to  deduce  that  property 
which  I  am  going  to  attribute  to  the  nerves,  however 
much  I  may  be  inclined  to  assent  to  Ludwig's  dictum 

^Academic   Discourse   delivered   before   the   University   of    Leipsic, 
May  21,  1898. 

2Second  Edition,  page  141. 


44  THE   SPECIFIC   ENERGIES. 

"that  a  nerve  is  indebted  for  its  energy  to  its  constitu- 
tion and  structure,"  and  for  a  change  in  its  energy  to  a 
corresponding  change  in  them. 

The  source  from  which  I  have  derived  my  views 
relative  to  the  mode  of  activity  of  the  nerve-fibers, 
lies  quite  remote  from  all  the  knowledge  we  now  have 
of  their  structure  and  of  their  chemical  and  physical 
properties,  and  I  am  therefore  perfectly  willing  that 
the  view  which  I  have  put  forward  as  a  contribution 
to  the  theory  of  nerve-activity  should  be  regarded 
only  as  a  conjecture. 

In  justification  of  my  position,  however,  I  may  add 
that  even  at  best  we  are  in  possession  only  of  con- 
jectures concerning  the  real  inner  nature  of  nerve- 
activity.  We  know,  thanks  to  Helmholtz,  that  any 
sudden  alteration  in  the  condition  of  the  nerve-fiber 
caused  by  some  stimulus,  is  propagated  along  the  fiber 
with  a  measurable  speed,  and  we  know  further  how 
great  this  speed  approximately  is.  But  the  exact  na- 
ture of  that  alteration,  and  the  exact  character  of  the 
process  propagated  along  the  fiber,  we  do  not  know. 
Dubois-Reymond's  classical  investigations  have  made 
us  acquainted  with  the  electro-motor  property  of  the 
nerve  in  its  various  conditions.  But  as  little  as  a  gal- 
vanic current  gives  us  an  explanation  of  the  peculiari- 
ties of  the  chemical  process  to  which  it  owes  its  origin, 
so  little  does  the  current  derived  from  a  nerve  give 
us  information  concerning  the  peculiarities  of  the 
chemical  change  in  the  nervous  substance.  The  as- 
sumption that  chemical  phenomena  are  the  gist  of  the 
process  which  we  are  wont  to  designate  as  the  activity 
of  the  nerve,  is,  of  course,  no  more  than  a  mere  con- 
jecture. But  in  making  such  a  conjecture  we  assert 


THEORY    OF    NERVE    ACTIVITY.  45 

concerning  the  nerve  nothing  more  than  what  might 
just  as  well  be  asserted  of  all  living  substances,  and 
nothing  is  said  which  would  characteristically  dis- 
tinguish the  life  of  the  nerve  from  the  life  of  any 
other  organ. 

In  fact,  life  is  still  as  much  of  an  unsolved  riddle 
as  it  was  when  the  so-called  mechanical  conception 
of  vital  phenomena  overthrew  the  vitalistic,  and 
awakened  by  its  brilliant  achievements  the  most  san- 
guine expectations,  foreshadowing  results  far  beyond 
what  has  even  yet  been  fulfilled,  valuable  and  fruitful 
as  this  has  been. 

To  whatever  point  the  physical  or  chemical  inves- 
tigation of  the  animal  organism  has  penetrated,  it  has 
always,  sooner  or  later,  come  upon  the  mysterious 
action  of  the  living  substance  of  those  elementary 
organisms  of  which  the  animal  and  the  human  body 
are  composed.  We  have  now  learned  modesty,  and 
from  having  once  believed  that  we  had  entered  the 
holy  of  holies,  we  now  acknowledge  that  we  have  as 
yet  scarcely  passed  the  portico  of  the  temple.  Can 
it  surprise  us  then  that  to-day  the  old  fallacious  doc- 
trine of  vital  force  which  we  imagined  had  been  defi- 
nitely vanquished,  should  again  rear  its  head  under 
new  names?  Let  us  confess  that  we  ourselves  are 
to  blame  for  this  because  in  the  first  exultation  of 
success  we  promised  more  than  we  were  able  to 
fulfill. 

Let  us  cease  considering  physiology  merely  as  a 
sort  of  applied  physics  and  chemistry  and  thus  avoid 
arousing  the  justifiable  opposition  of  those  who  be- 
lieve it  to  be  an  idle  task  to  seek  an  exhaustive  ex- 
planation of  the  living  from  the  dead.  Life  can  be 


46  THEORY    OF   NERVE   ACTIVITY. 

fully  understood  only  from  life,  and  a  physics  and  a 
chemistry  which  have  sprung  solely  from  the  domain 
of  inanimate  nature,  and  which  therefore  apply  solely 
to  inanimate  nature,  are  adequate  only  to  the  explana- 
tion of  such  things  as  are  common  to  the  living  and 
the  dead. 

This  is  very  much,  but  it  is  not  all,  and  I  am  fain 
to  paraphrase  here  the  words  of  a  brilliant  physicist3 
who  has  used  them  in  an  analogous  connection,  and 
say:  If  the  assertion  that  physiology  is  only  applied 
physics  and  chemistry  be  taken  to  mean  that  the 
laws  discovered  in  the  domain  of  physics  and  chem- 
istry are  sufficient  without  extension  and  generaliza- 
tion to  explain  fully  the  phenomena  of  life,  "we 
are,  in  my  opinion,  confronted  with  a  view  which 
is  in  all  respects  comparable  to  that  of  Thales,  who 
endeavored  to  explain  everything  from  the  proper- 
ties of  water.  Think  of  the  improbability  that  a  wide 
domain  of  experience  can  be  absolutely  exhausted 
by  a  narrower  one  previously  known."  If  every- 
thing that  took  place  in  nature  could  be  designated 
outright  as  physical  or  chemical,  whether  it  was  sub- 
sumable  under  the  present  known  laws  of  physics 
or  chemistry  or  not,  then  naturally  all  phenomena 
of  life  would  in  such  a  case  fall  within  the  domain 
of  physics  and  chemistry.  But  we  cannot  hoist  our 
flag  over  a  territory  where  we  have  never  as  yet  set 
foot,  much  less  explored. 

At  bottom,  it  was  not  the  mere  negation  of  vital 
force  at  this  juncture  that  secured  for  physiology  its 
brilliant  successes,  but  rather  the  concomitant  intro- 
duction into  biology  of  the  rigorous  methods  of  phys- 

«E.  Mach,  Die  Principien  der  Warmelehre,  p.  351. 


THEORY   OF   NERVE   ACTIVITY.  47 

ical  science  and  of  the  great  mass  of  apparatus  and 
appliances  which  had  been  created  by  those  methods; 
and  only  in  so  far  as  vitalism  persisted  in  employing 
unproductive  methods  for  treating  biological  problems 
did  it  do  real  harm  and  was  its  overthrow  of  real 
benefit.  In  fact,  every  .observed  attribute  of  life 
which  was  susceptible  of  immediate  physical  explana- 
tion had  already  been  physically  explained  in  the 
heyday  of  vitalism.  The  laws  of  the  lever  were 
applied  to  the  movement  of  the  human  members,  and 
the  movement  of  the  blood  attributed  to  the  con- 
traction of  the  muscles  of  the  heart,  even  at  a  time 
when  the  muscular  activity  itself  was  still  conceived 
in  characteristically  vitalistic  fashion.  Even  to-day 
we  cannot  explain  this  last-named  activity,  although  it 
is  one  of  the  most  palpable  and  most  obtrusive  of  the 
actions  of  living  things. 

The  impulse  to  resort  to  analogy  and  to  carry  over 
propositions  abstracted  from  one  domain  into  others 
is  so  great  that  there  can  be  no  fear  that  any  phe- 
nomenon of  life  will  long  remain  exempt  from  phys- 
ical or  chemical  explanation  after  physics  and  chem- 
istry have  supplied  the  requisite  means.  To-day, 
the  danger  of  precipitate  and  therefore  of  insuffi- 
cient physico-chemical  explanation  of  vital  phenom- 
ena is  perhaps  greater  than  the  danger  of  that  vital 
force  should  continue  to  be  employed  (to  use  a  cele- 
brated saying)  "as  the  comfortable  couch  where  rea- 
son is  quieted  upon  the  pillow  of  obscure  qualities." 

Even  the  mechanical  theory  of  life  has  not  been 
able  to  prevent  the  substitution  of  a  new  dogmatism 
for  the  old  vitalistic  creed,  and  in  adducing  a  strik- 
ing instance  of  this  fact  I  reach  the  real  subject  of 


48  THEORY    OF   NERVE   ACTIVITY, 

my  present  discussion. 


I  have  already  stated  that  the  process  which  is 
propagated  along  a  nerve-fiber  in  the  shape  of  a  so- 
called  excitation  is  in  its  real  nature  unknown  to  us. 
Nevertheless,  it  is  accepted  as  an  established  fact 
by  most  physiologists  to-day  that  this  excitation  is 
always  of  exactly  the  same  kind,  not  only  in  one 
and  the  same  nerve-fiber  but  in  all  nerve- fibers;  and 
that  it  can  consequently  undergo  alteration  only  with 
regard  to  the  strength  and  time  of  its  propagation, 
but  not  as  regards  its  quality;  and  that,  therefore, 
all  functional  differentiation  of  the  nerves  is  exclu- 
sively resident  in  either  their  central  or  their  peri- 
pheral terminal  apparatus.  So  thoroughly  convinced 
are  many  physiologists  of  the  truth  of  this  view,  that 
they  absolutely  refuse  to  consider  any  theory  which 
assumes  a  qualitative  variability  in  the  excitations 
which  pass  through  the  nerve-fibers.  And  they  do 
this  in  the  consciousness  that  they  are  supported  by 
the  authority  of  a  Helmholtz,  a  Dubois-Reymond, 
and  a  Bonders. 

But  let  us  examine  for  a  moment  the  meaning 
of  the  assertion  that  the  excitations  are  absolutely 
alike  in  all  nerve-fibers. 

If  it  were  possible  to  insert  a  portion  of  a  sensory 
nerve  into  the  path  of  a  motor  nerve,  and  to  con- 
nect the  former  with  the  latter,  fiber  for  fiber,  a 
cerebral  excitation  of  the  motor  nerve  would  pass 
unaltered  through  the  inserted  piece  of  sensory  nerve 
to  the  muscle,  which  it  would  forthwith  set  into 
activity.  Or,  if  we  could  cut  out  a  piece  of  the  optic 


THEORY    OF   NERVE   ACTIVITY.  49 

nerve  and  insert  in  its  place  a  piece  of  a  motor  nerve, 
and  combine  every  fiber  of  the  former  with  every 
fiber  of  the  latter,  functional  continuity  would  be 
restored  along  with  the  anatomical  continuity,  and 
the  perception  of  light  and  color  would  be  possible 
just  as  before. 

Finally,  let  us  imagine  the  optic  nerve  and  the 
auditory  nerve  severed,  and  each  brought  into  con- 
junction with  the  other  crosswise.  According  to  Du- 
bois  Reymondi,  we  should  in  such  a  case  hear  the 
lightning  with  the  eye  as  a  noise,  and  see  the  thun- 
der with  the  ear  as  a  succession  of  light-impressions. 

Of  such  a  character  are  the  consequences  that  flow 
from  the  assumption  that  the  functions  of  the  nerve- 
fibers  are  all  absolutely  alike.  The  impossibility  of 
actually  realizing  the  hypothetical  cases  which  have 
been  adduced  affect  in  no  wise  the  correctness  of 
the  conclusions  drawn  from  them. 


What,  now,  are  the  considerations  that  could  have 
led  to  the  enunciation  of  a  definite  opinion  regard- 
ing processes  which  are  still  involved  in  so  much 
mystery  for  us?  Carl  Ludwig  himself  once  consid- 
ered the  question  of  the  likeness  or  unlikeness  of  the 
nerve-fibers,  and  did  so  with  all  his  wonted  caution, 
but  he  finally  left  the  question  undecided,  as  did  also 
Johannes  Muller  in  his  time.  Since  then,  no  new 
facts  have  been  brought  to  light  which  could  have 
tended  to  confirm  the  theory  of  the  homogeneity  of 
the  nerve-fibers,  as  Ludwig  called  it.  For  the  ex- 
periments in  the  grafting  of  the  peripheral  termi- 
nals of  severed  nerves,  with  the  central  terminal  of 


50  THEORY    OF   NERVE   ACTIVITY. 

a  nerve  having  different  functions,  even  if  they  had 
been  successful,  could  not  have  decided  our  ques- 
tion. And  yet,  by  the  majority  of  physiologists  the 
theory  of  homogeneity  is  regarded  to-day  as  an  estab- 
lished truth. 

By  his  Investigations  in  Animal  Electricity  Dubois 
Reymond4  believed  he  had  "awakened  into  lifelike 
reality  the  hundred  years'  dream  of  the  physicists  and 
physiologists  regarding  the  identity  of  nervous  energy 
and  electricity,  even  though  in  a  slightly  changed 
form."  The  facts  which  he  adduced  have  been  con- 
firmed in  all  their  essential  points,  and  although  their 
interpretation  has  turned  out  to  be  different  from 
what  he  conjectured,  yet  the  opinion  which  he  cher- 
ished, according  to  which  the  essential  nature  of  nerv- 
ous activity  found  its  expression  in  electrical  phe- 
nomena, is  still  shared  by  many  physiologists  to-day. 
Now  this  view  was  in  its  time,  and  is  to-day,  so  far 
as  I  can  see,  the  principal  foundation  of  the  con- 
viction which  so  generally  obtains  in  the  scientific 
world  regarding  the  homogeneity  of  the  nerve-fibers 
and  of  their  excitations. 

When  we  set  a  nerve  in  excitation  at  any  point 
of  its  course  by  an  artificial  stimulus,  the  propaga- 
tion of  the  process  of  excitation  can  be  followed 
step  by  step  along  the  path  of  the  nerve  by  means 
of  a  galvanometer,  for  the  reason  that  the  electric 
behavior  of  the  nervous  substance  changes  precisely 
as  the  condition  of  the  nervous  substance  itself 
changes  in  passing  to  the  excited  state.  The  gal- 
vanometer then  shows  us  the  current  of  action,  or 
at  the  severed  terminus  of  the  nerve  the  so-called 

'Preface,  p.   15. 


THEORY   OF   NERVE   ACTIVITY.  51 

oscillation  of  the  current  of  injury.  It  was  rendered 
highly  probable  by  Dubois  Reymond  (and  later 
investigations  have  only  confirmed  the  conjecture) 
that  these  electrical  phenomena  are  characteristic  of 
all  nerves,  and  that  they  accompany  not  only  the 
excitations  which  have  been  produced  by  artificial 
stimuli,  but  also  such  as  are  disengaged  in  the  natu- 
ral way  from  the  central  or  peripheral  terminal  appa- 
ratus of  the  nerve-fiber.  If  now  the  electric  phe- 
nomena were  the  expression  of  the  real  inner  char- 
acter of  the  excitation  passing  along  the  nerve,  the 
homogeneity  of  the  latter  would  follow  immediately 
from  the  homogeneity  of  the  former;  and  different 
nerve-fibers  could  exhibit  different  behaviors  only 
with  regard  to  the  intensity  and  time  of  action  of 
the  excitation. 

It  was  afterwards  discovered  that  the  electric  phe- 
nomenon in  question  admitted  of  scarcely  any  other 
explanation  than  that  of  a  chemical  process  propagated 
along  the  excited  nerve.  Yet  even  this  discovery  could 
not  shake  the  theory  of  homogeneity. 

After  that  theory  had  once  taken  root,  the  identity 
of  the  chemical  process  was  deduced  immediately 
from  the  identity  of  the  electrical  behavior,  and  the 
idea  never  suggested  itself  that  we  might  with  just 
as  good  reason  infer  the  identity  of  two  chemical 
processes  from  the  identity  of  their  thermal  effects, 
or  the  identity  of  the  chemical  transformation  in  two 
galvanic  elements  from  the  identity  of  their  currents. 

The  electrical  phenomena  which  accompany  the  ex- 
citation of  the  nerve  furnishing  no  adequate  founda- 
tion for  the  the'ory  of  homogeneity,  the  next  natural 
support  likely  to  be  resorted  to  for  this  theory  is 


52  THEORY    OF   NERVE   ACTIVITY 

that  of  the  morphological  and  chemical  homogeneity 
of  the  nerve-fibers.  It  is  quite  true,  we  are  as  yet 
unable  to  distinguish  by  the  microscope  and  by  chem- 
ical reactions  every  motor  fiber  from  every  secretory 
fiber,  and  every  optic  fiber  from  every  auditory  fiber. 
But  the  cases  are  numberless  in  which  living  ele- 
mentary structures  having  different  functions  exhibit 
absolutely  the  same  behavior  when  subjected  to  known 
optical  or  chemical  tests. 

The  germs  of  quite  different  species  of  animals 
are  frequently  so  much  alike  as  to  be  confounded 
with  one  another;  and  the  germs  of  different  indi- 
viduals of  the  same  species  naturally  show  a  still 
greater  degree  of  similarity.  Yet  no  biologist  has 
the  least  hesitation  in  ascribing  to  each  individual 
germ  some  quite  specific  individuality,  some  personal 
idiosyncrasy,  so  to  speak,  of  inward  structure  or  mol- 
ecular constitution  by  virtue  of  which  a  perfectly 
definite  path  of  future  development  is  marked  out 
for  it. 

It  is  regarded  as  almost  certain  that  the  different 
functions  of  the  secretory  cells  of  the  various  glands 
are  attributable  to  the  physical  and  chemical  differ- 
ences of  their  vital  substance,  and  yet  in  many  cases 
it  would  be  quite  impossible  by  the  microscope  and 
micro-chemical  methods  at  our  command,  to  deter- 
mine the  actual  function  of  any  single  glandular  cell. 

It  was  shown  by  Max  Schultze  many  years  ago, 
and  recent  inquiries  have  confirmed  his  results,5  that 
while  the  pseudopodia  of  the  same  rhizopod  merged 
and  fused  perfectly  on  contact,  the  pseudopodia  of 

"Paul  Jensen,  "Ueber  individuelle  physiologische  Unterschiede 
zwischen  Zellen  der  gleichen  Art."  Pfliiger's  Archiv  fur  die  ges. 
Physiologic.  Bd.  LXIL,  p.  175.  1895. 


THEORY    OF    NERVE   ACTIVITY.  S3 

different  individuals  of  the  same  species  would  not 
fuse  on  being  brought  together.  Now,  if  the  pro- 
toplasm of  two  individuals  of  the  same  species  were 
absolutely  of  the  same  composition,  it  would  be  diffi- 
cult to  see  why  their  pseudopodia  should  not  behave 
with  regard  to  one  another  precisely  as  the  pseudo- 
podia  of  the  same  individual  do. 

We  are  obliged,  accordingly,  to  attribute  to  the 
living  substance  of  every  single  one  of  these  minute 
and  inferior  creatures,  specific  individual  properties, 
by  virtue  of  which  their  substance  is  distinguished 
from  the  substance  of  every  other  individual  of  the 
same  species;  although  there  cannot  be,  even  in  so 
patent  a  case  as  the  present,  the  remotest  thought 
of  directly  demonstrating  these  inferred  differences 
by  the  experimental  means  of  investigation  at  our 
command. 

But  if  a  distinctive  individual  stamp  must  be  im- 
puted to  every  one  of  the  countless  members  of  the 
same  rhizopod  species,  why  shall  some  such  distinc- 
tive mark  be  refused  to  the  elementary  organisms 
of  which  the  nervous  system  is  composed?  The  fact 
that  the  rhizopods  lead  an  independent  life,  while  the 
nerve-elements  are  rigorously  subordinated  parts  of 
a  more  highly  developed  organism,  is  no  reason 
whatever  for  our  not  doing  so,  seeing  that  each  indi- 
vidual nerve-fiber  is  connected  with  a  vast  and  most 
varied  host  of  vital  functions,  and  that  consequently 
it  can  be  highly  differentiated  according  to  the  prin- 
ciple of  the  division  of  labor;  whereas  no  such  divi- 
sion of  labor  can  come  into  consideration  in  the  case 
of  the  individuals  of  a  rhizopod  species. 

In  this  division  of  labor  of  our  organism  lies,  in 


54  THEORY    OF    NERVE   ACTIVITY. 

fact,  part  of  the  answer  which  I  should  give  to 
the  advocates  of  the  theory  of  homogeneity,  if  they 
were  to  ask  why  I  am  anxious  to  assume  heterogeneity 
in  places  where  the  assumption  of  homogeneity  ap- 
pears to  be  adequate  to  explain  the  function  of  nerve- 
fibers  as  simple  organs  of  conductivity.  The  argu- 
ment that  I  have  adduced,  they  would  contend,  proved 
at  most  that  the  sameness  of  all  the  fibers  cannot  now 
be  directly  demonstrated,  that  there  are  even  reasons 
for  suspecting  them  to  be  not  the  same,  but  that  in 
any  event  no  counterproof  to  their  theory  is  furnished. 
Even  the  wires  which  conduct  electricity,  they  would 
say  further,  may  be  put  to  very  different  uses,  and 
yet  the  electrical  phenomenon  in  the  conducting  wires 
is  qualitatively  the  same. 

The  fact  that  the  excitation  of  a  glandular  nerve 
produces  a  secretion,  while  that  of  a  muscle-nerve 
produces  a  movement,  is  sufficiently  explained  by  a 
difference  in  the  terminal  apparatus  upon  which  those 
nerves  act;  and  there  is  just  so  much  ground  and 
no  more  for  supposing  a  qualitative  difference  of 
excitation  to  result  from  a  difference  in  the  stimuli 
by  which  the  nerves  of  the  several  sense-organs  are 
excited.  The  further  fact,  they  would  continue,  that 
sound  is  able  to  excite  the  auditory  nerve  and  light 
the  optic  nerve  is  due  entirely  to  the  different  struc- 
ture of  the  apparatus  at  the  peripheral  end  of  these 
nerves, — one  apparatus  being  especially  adapted  for 
the  reception  of  sound-waves  and  the  other  for  the 
reception  of  light-waves  and  for  their  transformation 
into  nervous  excitation.  If  the  sound  were  to  strike 
directly  upon  the  auditory  nerve  itself,  and  not  on 
the  peripheral  apparatus,  if  the  light  were  to  fall  di- 


THEORY    OF   NERVE   ACTIVITY.  55 

rectly  upon  the  optic  nerve  itself,  these  nerves  would 
not  be  excited, — a  proof  that  the  so-called  specific 
excitability  of  the  various  sensory  nerves  is  not  due 
to  any  dissimilarity  of  the  latter,  but  entirely  to  the 
differences  of  the  terminal  apparatus  which  receive 
the  impression. 

In  answer  to  this  oft-repeated  argument,  it  must 
be  frankly  confessed  that  so  far  as  our  present  knowl- 
edge goes,  no  conclusion  whatever  follows  from  the 
varying  behavior  of  the  sense-organs  toward  differ- 
ent sensory  stimuli  in  favor  of  the  assumption  of  a 
specific  heterogeneity  of  the  sensory  nerve-fibers;  but 
neither  does  anything  follow  in  contravention  of  such 
an  assumption.  And  it  must  be  further  admitted  that 
considering  the  dissimilarity  in  results  which  follow 
upon  the  excitation  of  nerves  that  act  centrifugally 
according  as  they  set  a  muscle  or  a  gland  in  activity, 
no  conclusive  argument  is  forthcoming  either  in  favor 
or  in  contravention  of  the  homogeneity  of  these 
nerves. 

But  the  situation  assumes  a  different  aspect  when 
we  consider  the  manifold  results  to  which  the  excita- 
tion of  such  sensory  nerves  leads  as  have  not  their 
terminus  in  such  heterogeneous  organs  as  the  mus- 
cles or  the  glands,  but  all  end  in  the  brain.  For  in- 
stance, we  are  compelled  to  inquire  how  it  is  that 
the  excitation  of  one  nerve  brings  with  it  the  sensa- 
tion of  light  and  color,  that  of  another  the  sensa- 
tion of  sweet  and  sour,  that  of  a  third  the  sensation 
of  heat  and  cold,  while  at  the  same  time  all  these 
nerves  carry  to  the  brain  excitations  which  are  abso- 
lutely the  same  in  quality.  To  this  the  theory  of 
homogeneity  has  always  answered  without  the  least 


56  THEORY    OF   NERVE    ACTIVITY. 

ado  that  it  is  because  the  like  nerve-fibers  of  the 
tongue  and  of  the  eye  lead  to  unlike  nerve-cells  in 
the  brain,  some  of  them  to  cells  whose  specific  char- 
acter enables  them  to  take  up  the  excitatory  condi- 
tions that  correspond  to  the  sensations  of  taste,  others 
to  cells  which,  conformably  to  their  specific  function, 
respond  to  the  excitation  of  the  fiber  with  precisely 
that  physiological  process  whose  psychical  correlate 
is  a  sensation  of  light. 

And  here  finally  we  are  met  with  the  frank  conces- 
sion that  interior  commotion  of  the  nervous  substance 
which  we  call  excitation  or  activity  is,  at  least  in  the 
various  sensory  centers  of  the  brain,  specifically  dif- 
ferentiated, and  that  here  at  last  the  functional  homo- 
geneity reaches  its  termination. 


While  this  doctrine  was  taking  its  development, — a 
doctrine  according  to  which  all  the  nerve-fibers  are 
exactly  the  same  in  kind,  but  the  terminal  apparatus 
which  are  functionally  connected  with  them  are  differ- 
ent in  kind, — the  idea  necessarily  suggested  itself  of 
separating  the  nerve-fibers  as  a  particular  group  of 
elementary  structures  from  the  nerve-cells;  but,  even 
at  the  period  of  the  development  in  question,  it  would 
have  been  quite  admissible,  in  view  of  the  anatomical 
continuity  which  had  been  established  in  numerous 
instances  between  cells  and  fibers,  to  have  inquired 
by  what  right  physiologists  ascribed  to  the  cells  func- 
tions which  varied  in  character,  whereas  they  denied 
to  the  fibers  connecting  them  all  specific  dissimilarity 
whatever,  and  did  so  in  spite  of  the  fact  that  chem- 
ical and  physical  research  had  not  been  able  to  dis- 


THEORY    OF   NERVE   ACTIVITY.  57 

cern  any  more  characteristic  differences  in  the  sub- 
stance of  the  cells  than  it  had  in  the  axial  cylinder 
of  the  fibers. 

Since  that  time,  a  different  conception  of  the  ele- 
mentary structures  of  the  nervous  system  has  found 
almost  universal  acceptance.  According  to  this  the- 
ory, every  nerve-fiber  is  associated  in  such  wise  with 
a  nerve-cell  as  to  form  with  it  a  single  elementary 
organism  only ;  and  the  living  substance  of  that  organ- 
ism, which  is  collected  in  more  abundant  quantities 
about  the  nucleus  of  the  nerve-cell,  is  continued  into 
the  fibers.  Accordingly,  the  nerve-fibers  would  be 
integral  constituents  of  these  elementary  structures  of 
the  nervous  system,  or  "neurons"  as  they  are  called. 
On  this  theory,  the  idea  is  quite  natural  to  ascribe 
to  the  fibers  which  continue  the  cells  the  same  specific 
differences  which  physiologists  were  obliged  to  assign 
to  the  nerve-cells  of  the  various  cerebral  centers.6  But 
as  soon  as  we  do  this,  we  no  longer  have  before  us 
cells  which,  though  capable  of  performing  different 
tasks,  are  yet  connected  by  filaments  having  quite  the 
same  functions,  but  we  have  elementary  organisms 
whose  specific  or  individual  dissimilarity  extends  to 
their  remotest  filar  prolongations.  A  nerve-trunk  is 
no  longer  a  mere  bundle  of  conducting  wires  disen- 
gaging different  sorts  of  effects,  according  to  the 
kind  of  apparatus  with  which  they  are  connected  at 
their  termini  and  being  at  the  same  time  in  their  own 
specific  function  absolutely  of  the  same  kind;  but  it 
is  a  bundle  of  living  arms  which  the  elementary  organ- 
isms of  the  nervous  system  send  forth  for  the  pur- 

6I  offer  no  opinion  as  to  the  correctness  of  the  histological  doctrine 
of  neurons.  I  lay  it  at  the  foundation  of  the  present  discussion  be- 
cause my  theory  needs  some  definite  histological  substratum. 


58  THEORY    OF    NERVE    ACTIVITY. 

pose  of  entering  into  functional  connection  with  one 
another,  or  of  permitting  the  phenomena  of  the  out- 
side world  to  act  upon  them,  or  of  exercising  control 
over  other  organs  like  the  muscles  and  the  glands. 
And  in  each  one  of  these  arms  a  quite  special  kind 
of  life  is  active,  corresponding  precisely  to  the  neuron 
to  which  the  nerve-fiber  belongs.  The  conducting 
path  which  unites  a  sense-organ  with  the  cerebral  cor- 
tex, or  the  latter  with  a  muscle,  appears  as  a  chain 
of  living  individuals  of  which  every  member,  although 
always  dependent  upon  its  neighbors,  still  leads  a  sep- 
arate life,  the  specific  character  of  which  is  generally 
different  in  the  different  parts  of  the  nervous  system. 
Even  in  the  neurons  of  the  same  group  it  is  not  abso- 
lutely the  same,  but  bears  in  each  of  them  a  more  or 

less  individual  stamp. 

* 

*  * 

The  theory  of  the  homogeneity  of  the  excitatory 
process  in  all  the  nerve-fibers  involves  the  further 
assertion  that  this  process  remains  qualitatively  the 
same  in  one  and  the  same  fiber,  and  that  it  is  variable 
only  as  to  intensity  and  time  of  propagation. 

I  once  advanced  views- relating  to  the  processes  in 
the  nerve-apparatus  of  the  visual  organs  which  pre- 
supposed that  in  one  and  the  same  retinal  element 
different  processes  could  be  set  up  by  light-waves 
of  different  rates  of  vibration.  The  physiologists  de- 
clared such  a  view  inadmissible  inasmuch  as  more 
than  one  process  in  the  same  structural  element  would 
presuppose  more  than  one  conduction-process  in  the 
corresponding  fiber,  a  view  which  physiology  was 


THEORY    OF   NERVE   ACTIVITY.  59 

forthwith  compelled  to  repudiate.7  And  this  dogma, 
according  to  which  every  nerve-fiber  is  held  to  be 
capable  of  only  one  kind  of  excitation,  had  actually 
been  extended  also  to  the  nerve-cells.  True,  as  al- 
ready said,  physiologists  were  even  then  compelled 
to  ascribe  to  the  nerve-cells  of  the  different  sensory 
centers  different  functions;  but  in  one  and  the  same 
cell  the  excitation  was  said  to  be  of  unalterable  quality. 

It  was  no  less  an  authority  than  Helmholtz  who 
introduced  this  conception  into  the  physiology  of  sen- 
sation, and  to-day  his  disciples  still  esteem  the  doc- 
trine of  cerebral  cells  sensitive  only  to  red,  green, 
or  violet,  as  the  rarest  fruit  of  Johannes  Miiller's  doc- 
trine of  the  specific  energies  of  the  sensory  nerves. 
But  I  am  convinced  that  Johannes  Miiller  would  not 
have  accepted  such  a  view,  for  his  conception  of  biol- 
ogy was  thoroughly  monistic,  and  he  would  not  have 
denied  to  the  cell  of  the  brain  what  must  be  conceded 
to  the  lowest  unicellular  organism,  namely,  a  more  or 
less  wide  qualitative  variability  of  its  inner  life. 

Who  can  deny  that  the  chemical  changes  in  the 
substance  of  an  infusorian  vary  qualitatively  accord- 
ing to  the  changes  in  its  external  life-conditions;  for 
example,  in  food  material,  or  in  other  stimuli  acting 
upon  its  body?  And  even  granting  that  the  progres- 
sive division  of  labor  which  accompanies  the  increas- 
ing structural  complexity  of  the  animal  organism,  in 
general  brings  more  structural  uniformity  into  the  life 
of  the  individual  cells,  still  there  is  no  ground  for 
the  view  that  just  in  the  nerve-cell  this  uniformity 
can  become  as  complete  as  the  homogeneity  theory 

'Bonders,  "Ueber  Farbensysteme,"  Arch.    f.    Ophthalmol.,    XXVII. 
1881. 


60  THEORY    OF   NERVE   ACTIVITY. 

demands. 

Granting,  however,  the  possibility  of  qualitatively 
different  excitation-conditions  in  the  same  cell  (and 
in  the  fiber  springing  from  it),  then  there  is  opened 
for  the  theory  of  nerve-life  a  series  of  points  of 
view  which  are  quite  excluded  by  the  homogeneity 
theory. 

At  the  outset  it  follows  that  a  neuron  which  is  capa- 
ble of  various  kinds  of  activities,  will  possess  a  corre- 
spondingly complex  excitability,  that  is  to  say,  it  will 
vary  in  its  reactions  according  to  the  nature  of  the 
stimuli,  it  will  respond  by  one  or  another  of  its  habit- 
ual special  activities;  in  brief,  the  activity  of  the  neu- 
ron and  of  its  fiber  may  vary,  not  merely,  as  has  been 
supposed,  in  intensity  but  also  in  quality,  according 
to  the  nature  of  the  stimulus,  whether  this  be  exer- 
cised by  an  external  sense-organ,  or  by  an  adjacent 
neuron.  A  further  consequence  of  our  view  would 
be  that  the  effects  in  those  non-nervous  elementary 
organs  with  which  centrifugal  fibers  stand  in  functional 
connection,  might  also  vary  with  the  kind  of  excita- 
tion conducted  in  the  fiber. 

For  the  motor  fibers,  of  course,  there  is,  owing  to 
the  uniform  action  of  the  muscle-fiber,  no  apparent 
reason  for  such  a  view.  It  is  different,  however,  with 
the  nerve-fibers  which  govern  the  activity  of  a  gland. 
The  view  now  generally  accepted  is  that,  in  conform- 
ity with  their  unalterable  homogeneity  of  excitation, 
these  secretory  fibres  can  influence  the  activity  of 
their  dependent  gland-cells  only  quantitatively.  But 
how  would  it  be  if,  according  to  the  nature  of  the 
excitation  given  by  the  nerve-fiber,  the  chemical  proc- 
esses in  the  secretory  cells  were  different,  and  con- 


THEORY    OF    NERVE    ACTIVITY.  61 

sequently  the  nervous  system  could  affect,  within  cer- 
tain definite  limits,  the  quality  ol  the  secretion  fur- 
nished by  one  and  the  same  cell? 

And  would  not  similar  views  hold  in  regard  to  the 
so-called  trophic  activities  of  centrifugal  nerves?  In- 
asmuch as  these  activities  do  not,  as  in  the  case  of 
the  motor  or  secretory  nerves,  immediately  reveal 
themselves  by  easily  demonstrable  movements,  they 
have  hitherto  remained  rather  within  the  domain  of 
conjecture  than  in  that  of  safely  ascertained  facts. 
If,  however,  the  nervous  system  exerted  an  imme- 
diate influence,  not  merely  on  the  motor  and  secre- 
tory, but  also  on  the  other  elementary  organs  of  the 
body  (e.  g.,  on  certain  epithelia,  on  the  developing 
cells  of  the  ovary,  etc.),  then  here,  too,  the  answer 
to  the  question  whether  such  an  influence  were  varia- 
ble only  according  to  quantity  or  also  according  to 
quality,  would  be  of  far-reaching  influence. 

But  let  us  turn  back  to  the  activities  which  the 
excitation  of  a  neuron  exercises  on  those  other  neu- 
rons with  which  it  is  connected. 

If,  as  histology  teaches  us,  a  sensory  fiber  enter- 
ing the  spinal  cord  divides  into  an  ascending  branch 
and  a  descending  branch,  and  from  these  latter  there 
branch  off  the  so-called  collaterals  which  finally  stand 
in  relation  with  other  neurons  (it  matters  not  whether 
through  direct  contact  or  through  connection)  ;  if 
finally  every  one  of  these  neurons  by  its  branching 
stands  in  functional  relation  with  still  others,  and 
so  on;  then,  from  a  purely  anatomical  standpoint, 
there  exists  for  an  incoming  excitation  an  incalculable 
multiplicity  of  paths  through  the  central  nervous  sys- 
tem. If  now  an  excitation  which  has  seized  a  neuron, 


62  THEORY    OF    NERVE   ACTIVITY. 

should  pass  on  indifferently  to  all  the  other  neurons 
with  which  the  first  is  functionally  connected,  there 
would  result  an  exceedingly  widespread  diffusion  of 
the  excitation  entering  through  a  sensory  fiber  or 
coming  from  a  neuron  to  the  cerebral  cortex,  a  dif- 
fusion such  as  is  not  known  to  exist,  or,  at  the  most, 
is  only  approximated  to  in  motor  effects  under  patho- 
logical conditions. 

It  must  consequently  be  assumed  that  the  excita- 
tion of  a  fiber  does  not  take  indifferently  all  the 
anatomically  given  ways,  but  selects  predominantly 
certain  determined  paths,  diffusing  itself  in  the  others 
only  in  a  more  or  less  enfeebled  manner  or  only  ex- 
ceptionally; and  the  question  hence  arises:  What  is 
the  determining  factor  for  this  choice,  and  for  the 
varied  ratio  of  the  strengths  with  which  the  excita- 
tion propagates  itself  along  the  many  possible  paths? 

The  homogeneity  theory  finds  the  answer  in  the  dif- 
ferent degree  of  excitability  and  conductivity  of  the 
individual  paths,  and  in  the  different  amounts  of 
resistance  offered  to  passage  from  one  neuron  to 
another.  As  for  the  further  diffusion  this  is  made 
to  depend  entirely  on  the  strength  of  the  incoming 
stimulus. 

Numerous  facts  from  the  sensory  and  motor  terri- 
tories of  nerve-life  teach  us  that  the  innervation  issu- 
ing from  a  neuron  can  diffuse  itself  in  the  nervous 
system  very  differently  according  as  certain  other 
excitations  take  place  at  the  same  time.  For  exam- 
ple, though  the  stimulus  be  the  same,  a  reflex  move- 
ment is  sometimes  reinforced  and  sometimes  inhibited 
by  excitations  issuing  simultaneously  from  another 
place  on  the  periphery  of  the  body  or  from  the  brain. 


THEORY    OF    NERVE    ACTIVITY.  63 

Accordingly,  the  homogeneity  theory  accepts  the  view 
that  resistance  to  conduction  in  a  neuron  can  some- 
times be  increased  and  sometimes  lessened  by  excita- 
tions which  reach  the  same  neuron  from  another 
direction,  in  other  words  that  sometimes  a  so-called 
path-breaking,  sometimes  an  arrestation  takes  place; 
but  it  does  not  further  explain  how  excitations  which 
are  said  to  be  always  of  the  same  kind  and  to  differ 
only  quantitatively,  can  at  one  time  operate  on  the 
neuron  so  as  to  promote,  and  at  another  time  so  as 
to  arrest,  its  function. 

Everything  is  seen  in  a  different  light,  however, 
as  soon  as  a  qualitative  variability  of  the  conducted 
excitation,  and  also  a  qualitatively  different  excita- 
bility of  the  conducting  paths,  are  admitted.  If  the 
individual  nerve-fiber  is  suited  for  the  taking  up 
and  transmission  of  definite  qualities  of  excitation, 
either  preferentially  or  exclusively,  then  the  path 
which  is  taken  by  an  excitation  is  coincidently  deter- 
mined by  the  quality  of  that  excitation. 

As  a  report  is  principally  taken  up  and  circulated 
by  those  who  take  a  special  interest  in  it,  that  is 
to  say,  the  paths  of  its  spreading  depend  on  the 
nature  of  its  contents,  so  to  a  definite  afferent  excita- 
tion those  neurons  will  react  preponderatingly  whose 
peculiar  nature  precisely  corresponds  to  that  excita- 
tion. 

The  mutual  relations  of  neurons  will  then  depend 
not  merely  upon  their  anatomical  arrangement,  but 
also  on  their  degree  of  internal  structural  affinity. 
And  as  one  and  the  same  fiber  need  not  be  adapted 
merely  to  one  kind  of  excitation,  but  may  be  adapted 
to  a  certain  number  (though  within  a  narrow  range), 


64  THEORY    OF    NERVE   ACTIVITY. 

so  not  only  will  the  same  path  be  able  to  conduct 
various  kindred  qualities,  but  the  excitation  issuing 
from  the  same  neuron  will  be  able,  according  to  its 
particular  quality,  to  penetrate  various  parts  of  the 
nervous  system. 

If,  further,  excitations  should  be  simultaneously 
brought  to  the  same  neuron  by  two  of  its  neigh- 
bors, then  according  to  the  homogeneity  theory  these 
excitations  could  on  meeting  only  strengthen  or 
weaken  each  other.  According  to  our  view,  how- 
ever, the  two  excitations  could  be  of  different  kinds, 
and  from  their  meeting  in  the  same  substance  might 
originate  a  new  quality,  which  would  indeed  be  closely 
related  to  the  two  single  excitations,  but  not  like 
either. 

And  generally  the  whole  life  and  being  of  the  nerv- 
ous system,  its  ontogenesis  and  phylogenesis,  appear 
in  a  totally  different  light  as  soon  as  we  give  up  the 
dogma  of  the  absolutely  homogeneous  function  of  all 
nerve-fibers,  and  ascribe  to  the  individual  fiber-groups 
characters.  For  that  dogma  excludes  from  the  neu- 
ron every  capability  for  development  and  improve- 
ment, in  so  far  as  such  capability  is  not  already  inborn 
and  in  so  far  as  it  is  not  a  mere  augmentation  of  its 
excitational  or  vital  process,  which  latter  is  from  the 
beginning  to  the  end  of  its  life  supposed  to  be  peculiar 
and  unalterable. 

Rightly  have  the  opponents  of  the  doctrine  of  the 
specific  energies  of  the  sensory  nerves  pronounced 
against  the  view  of  a  life-long  unalterable  constancy 
of  function  of  the  nerves,  but  they  went  too  far,  as 
I  conceive,  when  they  contested  the  congenitally  dif- 
ferent and  special  nature  of  the  individual  sensory 


THEORY    OF    NERVE    ACTIVITY.  65 

nerves,  accepted  the  indifference  of  function  of  all 
sensory  fibers  of  the  new-born,  and  regarded  all  func- 
tional differences  of  nerve-fibers,  which  are  the  phylo- 
genetic  acquisition  of  innumerable  generations,  merely 
as  the  result  of  an  adaptation  to  heterogeneous,  indi- 
vidual sensory  stimuli  during  the  post-embryonic 
period. 

Of  course  after  birth  the  influences  of  the  external 
world  belong  to  the  conditions  of  the  further  normal 
development  of  the  whole  body,  and  the  sensory  stim- 
uli especially  are  indispensable  conditions  of  devel- 
opment of  the  nervous  apparatus  of  our  sense-organs. 
But  light,  for  example,  does  not  find  in  the  eye  of 
the  new-born  babe  a  nerve-substance  from  which, 
so  to  speak,  anything  whatever  can  be  made;  in  other 
words,  a  substance  which,  if  it  could  be  transposed 
from  the  eye  into  the  ear  or  into  the  tongue  could 
be  educated  by  the  sound-waves  to  a  medium  of  audi- 
tory sensations,  or  by  gustatory  stimuli  to  be  a  me- 
diurri  •  of i  taste-sensation. 

As  the- germ  sprouting  from  the  earth  needs  light 
to  become  a  green  plant,  so  in  the  new-born  babe 
the'  neuron  in  the  eye  needs  light,  and  the  neuron 
in  the  ear  the  sound  stimulus,  to  complete  its  course 
of  development;  but  just  as  light  never  makes  the 
fungus  green,  so  it  could  never  make  the  neurons 
of  the  ear  to  see  if  they  should  be  transplanted  into 
the  eye.  As  I  take  it,  the  neurons  of  our  eye  are 
not  merely  educated,  but  are  born  for  seeing,  and  like- 
wise those  of  our  ear  for  hearing. 

This,  however,  does  not  exclude  the  fact  that, 
within  their  own  narrow  congenital  limits  of  exist- 
ence and  action,  they  are  capable  of  further  indi- 


66  THEORY    OF    NERVE   ACTIVITY. 

vidual  development.  And  the  same  holds  good  (some- 
times more,  sometimes  less)  of  all  parts  of  our  nerv- 
ous system.  It  is  true,  the  farther  back  in  the  im- 
measurably long  developmental  series  of  the  animal 
organism  a  given  part  of  it  can  be  traced,  the  more 
fast  and  sharp  is  the  congenital  stamp  of  its  func- 
tion, and  the  less  capable  does  it  appear  of  trans- 
formation and  development  in  the  course  of  its  fur- 
ther life.  But  the  cerebral  cortex  is  reckoned  among 
the  phylogenetically  youngest  parts  of  our  nervous 
system,  and  its  neurons  belong,  as  it  seems,  to  those 
elementary  bodily  organs  which  in  post-natal  life  are 
afforded  the  relatively  widest  sphere  of  individual 
action  under  the  influence  of  impinging  stimuli.  Now, 
how  is  such  a  development  conceivable  if  the  internal 
activity  of  a  nerve-fiber  or  a  nerve-cell,  in  brief  a 
neuron,  is  to  be  always  of  one  and  the  same  kind? 

What  is  it  then  that  a  neuron  of  our  cortex  under 
normal  circumstances  experiences?  In  other  words, 
of  what  do  the  stimuli  which  encounter  it  and  deter- 
mine its  internal  activities,  consist?  Under  constant 
conditions  of  nutrition,  these  are  mainly  the  excita- 
tions conducted  to  it  from  those  other  neurons  which 
stand  in  relation  to  it  by  means  of  the  nerve-fibers. 
If,  however,  these  nerve-fibers  always  conduct  to  it 
only  the  same  kind  of  excitation,  have,  so  to  speak, 
only  one  note  to  their  lyre,  and  therefore  the  stimuli 
which  the  neurons  experience  throughout  life  are  the 
same  and  are  variable  only  in  quantity  and  time,  then 
the  reaction  of  the  neuron  will  also  always  be  one 
of  the  same  kind,  and  the  afferent  stimulus  can  only 
liberate  in  the  nerve-cell  forever  the  same  activity. 
And  if,  as  the  homogeneity  theory  concedes,  the  lat- 


THEORY    OF    NERVE    ACTIVITY.  67 

ter  could  be  different  in  the  different  nerve-cells,  still 
in  one  and  the  same  cell,  and  in  so  far  as  it  depends 
upon  the  afferent  excitations,  it  would  remain  the 
same  its  whole  life  long. 

It  will  be  altogether  different,  however,  if  these 
excitations  vary  qualitatively,  according  to  the  nature 
of  the  neighboring  neurons  from  which  they  come, 
or  if  the  afferent  excitation  from  one  and  the  same 
neuron  may  vary  within  certain  qualitative  limits. 
Then  a  more  or  less  rich  multiplicity  of  excitations 
will  take  the  place  of  the  just-mentioned  monotony 
that  the  neuron  experiences  from  its  neighbors,  and, 
as  this  neuron  is  in  its  turn  capable  of  heterogeneous 
activities,  there  is  also  opened  to  it  the  possibility  of 
reacting  to  different  impulses  in  different  ways. 

The  nature  of  this  reaction  will,  of  course,  also  be 
determined  by  the  inborn  individuality  of  the  neuron ; 
but  of  the  entire  stock  of  innate  qualities  which  it 
brings  with  it  from  birth  those  will  be  most  fully 
developed  in  the  course  of  its  life  to  whose  develop- 
ment the  neuron  is  most  frequently  or  most  strongly 
excited  by  its  neighbors.  Or,  briefly  stated,  the  neu- 
ron will  possess  the  capability  of  qualitative  and  not 
merely  of  quantitative  development,  which  last  would, 
according  to  the  homogeneity  theory,  alone  be  possible 
to  it. 

According  to  its  place  in  the  nervous  system,  its 
more  or  less  manifold  relations  to  other  neurons  and 
its  inborn  structure,  this  subsequent  development  will 
be  more  or  less  many-sided,  and  the  doctrine  of  the 
homogeneity-theory  that  the  sameness  of  excitation 
which  the  neurons  experience  conditions  a  correspond- 
ing uniformity  in  their  further  development,  may  per- 


68  THEORY    OF    NERVE   ACTIVITY, 

haps  approximately  hold  for  entire  large  groups  of 
neurons.  On  the  other  hand,  however,  all  experience 
or  training  both  sensory  and  motor, — in  brief,  every- 
thing that  can  be  called  conscious  or  unconscious  mem- 
ory in  the  widest  sense  of  the  word, — is  to  my  mind 
not  conceivable  unless  the  living  substance  of  the 
nerve-cells  and  fibers  is  capable  of  a  qualitatively  vari- 
able development. 

I  have  sought  in  vain  in  the  writings  of  those  sup- 
porters of  the  homogeneity  theory  who  have  occu- 
pied themselves  with  considerations  concerning  the 
physiological  foundations  of  nutrition  and  exercise, 
for  a  satisfactory  conception  of  the  subject.  For 
an  explanation  of  the  development  of  the  central 
nervous  system  corresponding  to  the  physical  devel- 
opment, we  are  with  reason  directed  to  the  possi- 
bility of  the  origin  of  new  connections  between  the 
neurons,  to  alterations  of  excitability  and  conductiv- 
ity in  the  paths  already  provided,  to  the  opening  and 
the  increasing  erosion  of  certain  old  paths  by  use, 
etc.  On  all  these,  old  or  new,  pervious  or  impervious 
paths,  however,  that  which  is  conducted  through  the 
nerve-fibers  still  remains  (according  to  the  homo- 
geneity-theory) always  the  same,  and  everywhere  it 
is  a  matter  only  of  moreness  or  lessness  and  of  vari- 
able velocity.  The  whole  nervous  system,  according 
to  this  theory,  appears  like  a  land  whose  numerous 
communities  are  connected  by  a  richly  developed  net- 
work of  road,  on  which  latter,  however,  always  and 
everywhere,  only  one  and  the  same  kind  of  wares  is 
transported. 

Writers  love  to  compare  the  nerve-fibers  with  tele- 
graph or  telephone  wires,  and  they  will  consequently, 


THEORY   OF   NERVE   ACTIVITY. 


69 


perhaps,  point  to  the  endless  multiplicity  of  things 
which  can  be  transmitted  through  wires  of  exactly 
the  same  kind.  The  comparison  is  seductive,  for  if 
spun  out  farther  it  seems  suited  to  solve  all  difficul- 
ties at  a  single  stroke. 

In  place  of  the  undoubtedly  "obscure"  specific  or 
individual  "qualities"  of  the  nervous  processes  of 
which  I  have  spoken,  appears  a  multiplicity  of  oscil- 
lations of  different  temporal  and  spatial  form,  of 
which  the  nerve-substance  is  the  mere  vehicle.  But 
all  come  finally  to  exactly  the  same  result  with  this 
comparison  as  I  do.  For  it  must  be  admitted  that 
neither  in  all  nerve-fibers  is  the  same  oscillation-form 
always  transmitted,  nor  is  every  individual  nerve-fiber 
susceptible  of  all  the  oscillation-forms  which  are  pos- 
sible to  the  nerve-substance  generally,  but  only  of 
those  to  which  it  can  respond. 

What  we  have  named  the  specific  energy  of  the 
fibers  or  cells  reappears  here  as  special  resonance- 
capacities  corresponding  to  definite  oscillation-forms. 
What  we  formerly  called  an  inborn,  acquired  or  indi- 
vidual characteristic,  becomes  here  the  pitch;  and,  as 
with  us,  the  specific  excitabilities,  so  here  the  reso- 
nance and  previous  attunement  of  the  neurons  deter- 
mine the  paths  in  the  nervous  system  which  a  given 
oscillation-form  shall  enter  upon. 

We  accordingly  acquire  only  another  mode  of  ex- 
pression for  one  and  the  same  thing;  and,  as  I  con- 
ceive, one  not  corresponding  so  well  to  the  facts, 
inasmuch  as  it  takes  no  account  of  that  which  in  an 
entirely  unique  way  characterizes  all  life,  namely, 
metabolism,  that  chemical  change  in  the  living  sub- 


70  THEORY    OF   NERVE   ACTIVITY. 

stance  whose  qualitative  differences  it  is  at  present 
(and  may  be  forever)  impossible  to  express  by  purely 
quantitative  spatial  and  temporal  terms. 

From  all  that  has  been  said  it  immediately  follows 
that  I  not  only  agree  with  the  teaching  of  Johannes 
Muller,  but  would  like  to  see  the  scope  of  his  concep- 
tion much  broadened.  The  specific  energies  are  in 
my  opinion  a  phylogenetically  acquired  heirloom,  not 
merely  of  the  sensory  nerves,  but  more  or  less  of 
all  neurons,  of  their  fibers  as  well  as  of  their  cells. 
But  I  consider  that  the  inheritance  allotted  to  the 
individual  neuron  is  by  no  means  so  sparing  and 
uniform  as  was  assumed  in  the  case  of  the  cells  of 
the  sensory  centers,  and  further  that  it  was  not  be- 
queathed with  a  codicil  that  the  heir  should  not  add 
any  newly  acquired  riches  to  his  inheritance. 


INDEX 


Acquired  energy  of  the  nervous 
system,  70;  properties  of  an  or- 
ganism, 15. 

Analogy,  41,    47. 

Animals  born  precocious,  21;  not 
unconscious  machines,  20. 

Apparatus  of  memory,  10;  ter- 
minal nerve,  55;  sense-organs, 
65. 

Aristotle,  28. 

Attunement  of  the  neurons,  69. 

Babe,  new-born,  not  a  completed 
structure,  36. 

Biology,   28. 

Body  and  mind,  functional  inter- 
dependence of,  3  et  seq. 

Book,  the  brain  a  closed,  40. 

Brain,  human,  at  birth  virgin  sub- 
stance, 37. 

Central  nervous  system,  develop- 
ment of,  68. 

Cerebral  cortex,  62,  66;  potency, 
23. 

Commander-in-chief,    the    will,    11. 

Concepts  or  ideas,  8. 

Congenital   limits   of   neurons,     65. 

Conjecture,   44. 

Consciousness  and  material  mech- 
anism, 2;  phenomena  of,  4; 
functional  interdependence  of 
matter  and,  6;  individual  and 
race,  22;  compared  to  a  work- 
man, 40. 


Determining  factor  in  the  activi- 
ties of  neurons,  the,  62. 

Dogma  and  the  homogeneity  the- 
ory, 59  and  64. 

Donders,   48 . 

Dubois-Reymond,  44,  48.  49,  50 
and  51. 


Electric  current,  26;  phenom- 
enon and  chemical  process,  51. 

Egg  shell,  things  learned  in  the, 
19. 

Elemental  memory,  23. 

Empsychosis,  2. 

Enigma  of  life,  32. 

Evolution  and  memory,  18. 

Excitability,   complex,    60. 

Filial  organism,  16. 

Fixed   formation   of   the   race,   22. 

Force  of  habit,  unconscious  mem- 
ory, 12. 

Function  denned,  4. 

Functional  differentiation  of  the 
nerves,  48. 


Galvanometer,   50. 
Germ  memory,  17. 
Germinal    vessels,    15;    cells    and 
memory,   16. 


Helmholtz,  44,    48,     59. 
Homogeneity      theory  •    explained, 
48    et    seq.;    62.    66' 


INDEX 


Idiosyncrasy  of  inward  structure, 
52. 

Immortality  as  unconscious  mem- 
ory, 23. 

Individual  consciousness,  22;  en- 
ergy, 36;  and  cerebral  cells,  39; 
properties,  53. 

Inherited  energy,   38. 

Instinct  and  race  memory,  20; 
as  predisposition,  22. 

Innate  function,   32. 

Language,  the  memory  of  man- 
kind, 23. 

Lever,  laws  of  a,    47. 
Light  and  color,  26,  34. 
Ludwig,  Carl,  43,    49. 

Mach   (note),   46. 

Machine,  unconscious,  20;  the 
human  body  not  a,  31. 

Material  process,  3;  of  memory,  8. 

Mechanical  conception  of  vital 
phenomena,  45. 

Memory,  6,  7,  8,  10,  12,  16,  23,  68. 

Mirror  of  consciousness,  5. 

Molecular  and  atomic  structure, 
30. 

Monistic  conception  of  biology,  59. 

Mueller,  Johannes,  25,  27,  28,  33, 
34,  49,  59,  and  70. 

Multiform  potency  and  specific  en- 
ergy, 35. 

Mutual  relations  of  neurons,    63. 

Nervous  system,  14. 

Neurologist,  4. 

Neurons,    57,     58,     60;     congenital 

limits  of,    65. 
Nocturnal    memory,    9. 
Nutrition,  36. 

Ontogenesis,  64 
Optic  nerve,  26. 
Perception,  10. 

Phylogenesis  of  the  nervous  sys- 
tem, 64. 


Physiology,  25,  45. 
Psychical    correlate    of    physiolog- 
ical   process,    56. 
Psychological  inquiries,   2,   3. 

Quality  and  quantity  of  excita- 
tion of  a  neuron,  61,  63;  in- 
nate, 67. 

Race  inheritance,  14;  memory  and 
instinct,  20. 

Reminiscences  in  old  age,   17. 

Repetition  of  function  and  sec- 
ond nature,  38. 

Reproduction  of  organic  process, 
13. 

Reproductive  faculty  of  the  ce- 
rebral substance,  23. 

Resonance-capacities  of  the  neur- 
ons, 69. 

Schultz,  Max,  52. 

Scientific  analysis,   29. 

Second  nature,    19. 

Sensation,  3. 

Sense  memory,  6,  7. 

Soul  and  brain,  the,  33;  inner  life 

of  the,  2. 

Sound  and  light,  54. 
Specialization    and    memory,    21. 
Specific     energy     of     the     sensory 

nerves,  25,  27,  30,  35,  58,   64,    69. 
Spiritual   and   material   facts,    5. 

Telegraph  or  telephone  wires,  an- 
alogy of,  68. 

Thales,  46. 

Theory  of  nerve  energy,    43, 

Tool-house  of  consciousness,  40. 

Traditions,  the  memory  of  man- 
kind, 23. 

Truth  revealed,  19. 

Unconscious    memory,    8,    18,    23. 

Virgin  substance  of  the  brain,  37. 

Visual  organs,  nerve-apparatus  of, 
58. 

Vital  phenomena,  mechanical  con- 
ception of,  45 


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